diff --git a/crates/perry-codegen/src/codegen/mod.rs b/crates/perry-codegen/src/codegen/mod.rs
index e553960ef7..29884ea3b7 100644
--- a/crates/perry-codegen/src/codegen/mod.rs
+++ b/crates/perry-codegen/src/codegen/mod.rs
@@ -131,6 +131,15 @@ pub fn compile_module(hir: &HirModule, opts: CompileOptions) -> Result<Vec<u8>>
     // becomes part of every emitted global so multi-module programs
     // don't collide on `.str.0.handle`.
     let mut strings = StringPool::with_prefix(module_prefix.clone());
+    // #5247: install per-module source-location context for the dynamic
+    // call-dispatch throw path, but only under `--debug-symbols` (which sets
+    // `opts.debug_locations` + `opts.module_source`). Off by default — no
+    // source clone, no per-call emission.
+    if opts.debug_locations {
+        if let Some(src) = opts.module_source.clone() {
+            strings.set_debug_location_ctx(Some((hir.name.clone(), src)));
+        }
+    }
 
     // Class lookup table for `Expr::New`. Indexed by class name —
     // the HIR has unique names per module.
diff --git a/crates/perry-codegen/src/codegen/opts.rs b/crates/perry-codegen/src/codegen/opts.rs
index c82fed6a9a..569643d804 100644
--- a/crates/perry-codegen/src/codegen/opts.rs
+++ b/crates/perry-codegen/src/codegen/opts.rs
@@ -366,6 +366,20 @@ pub struct CompileOptions {
     /// Without this, side-effect-only dynamic-import targets fail at
     /// link with `Undefined symbols: ___perry_ns_<prefix>`.
     pub is_dynamic_import_target: bool,
+
+    /// #5247: emit source-location tracking for the dynamic call-dispatch
+    /// throw path (`X is not a function`). Gated by the CLI `--debug-symbols`
+    /// flag; default `false` so release builds are byte-identical and incur
+    /// no per-call overhead. When `true` (and `module_source` is present),
+    /// each dynamic method-call dispatch is preceded by a
+    /// `js_set_call_location(file, line)` so the thrown TypeError's `.stack`
+    /// shows `at <file>:<line>`.
+    pub debug_locations: bool,
+    /// #5247: this module's original source text, used at codegen to resolve a
+    /// `Call`'s `byte_offset` to a 1-based line number. Only set when
+    /// `debug_locations` is on (avoids cloning source for every module in the
+    /// common build). `None` falls back to the `<anonymous>` frame.
+    pub module_source: Option<String>,
 }
 
 /// Issue #100: one entry in a module's namespace-population list.
diff --git a/crates/perry-codegen/src/collectors/hir_facts.rs b/crates/perry-codegen/src/collectors/hir_facts.rs
index 88d520c0e1..80299ea839 100644
--- a/crates/perry-codegen/src/collectors/hir_facts.rs
+++ b/crates/perry-codegen/src/collectors/hir_facts.rs
@@ -652,6 +652,7 @@ mod tests {
             callee: Box::new(Expr::FuncRef(7)),
             args: vec![arg, Expr::Integer(0), Expr::Integer(100)],
             type_args: vec![],
+            byte_offset: 0,
         };
         // let src = undefined; src = obj.value;       (disqualified seed)
         // const xx = clamp3(src, 0, 100);             (clamp-admitted)
diff --git a/crates/perry-codegen/src/collectors/pointer_locals.rs b/crates/perry-codegen/src/collectors/pointer_locals.rs
index 245f86fa95..d6df185ab5 100644
--- a/crates/perry-codegen/src/collectors/pointer_locals.rs
+++ b/crates/perry-codegen/src/collectors/pointer_locals.rs
@@ -775,6 +775,7 @@ mod tests {
                 callee: Box::new(Expr::FuncRef(1)),
                 args: vec![Expr::LocalGet(2)],
                 type_args: Vec::new(),
+                byte_offset: 0,
             }))],
             captures: Vec::new(),
             mutable_captures: Vec::new(),
diff --git a/crates/perry-codegen/src/expr/calls.rs b/crates/perry-codegen/src/expr/calls.rs
index 05f1131339..4e6b727203 100644
--- a/crates/perry-codegen/src/expr/calls.rs
+++ b/crates/perry-codegen/src/expr/calls.rs
@@ -47,6 +47,39 @@ use super::{
     I18nLowerCtx,
 };
 
+/// #5247: under `--debug-symbols`, emit a `js_set_call_location(file, line)`
+/// runtime call right before a dynamic method dispatch so the
+/// "X is not a function" throw path can render `at <file>:<line>` in the thrown
+/// TypeError's `.stack`. Resolves the *pending* call byte offset (recorded by
+/// the `Expr::Call` dispatcher) → `(file, line)` via the module's installed
+/// debug-location context. No-op (no IR emitted) when the context is absent
+/// (default build) or the pending offset is 0 (synthesized call).
+///
+/// Called at the dispatch emission site (after the call's arguments are
+/// lowered) with the offset the dispatcher captured at entry — before any
+/// nested-call argument overwrote the shared pending offset — so the location
+/// reflects the OUTER call, not its last-lowered argument.
+pub(crate) fn emit_call_location_at(ctx: &mut FnCtx<'_>, byte_offset: u32) {
+    let Some((file, line)) = ctx
+        .strings
+        .call_location_for(byte_offset)
+        .map(|(f, l)| (f.to_string(), l))
+    else {
+        return;
+    };
+    let file_label = emit_string_literal_global(ctx, &file);
+    let file_len = file.len();
+    let blk = ctx.block();
+    blk.call_void(
+        "js_set_call_location",
+        &[
+            (PTR, &file_label),
+            (I64, &file_len.to_string()),
+            (I32, &line.to_string()),
+        ],
+    );
+}
+
 /// #2013/#3146: emit a setup-time `validateString` call. `value_box` is the
 /// original NaN-boxed value; `name` is the static argument name node uses in
 /// the error (`"algorithm"` for `createHash`, `"hmac"` for `createHmac`'s
@@ -2369,7 +2402,12 @@ pub(crate) fn lower(ctx: &mut FnCtx<'_>, expr: &Expr) -> Result<String> {
         }
 
         // -------- Calls --------
-        Expr::Call { callee, args, .. } => {
+        Expr::Call {
+            callee,
+            args,
+            byte_offset,
+            ..
+        } => {
             for arg in args {
                 super::downgrade_buffer_aliases_in_expr(
                     ctx,
@@ -2377,6 +2415,16 @@ pub(crate) fn lower(ctx: &mut FnCtx<'_>, expr: &Expr) -> Result<String> {
                     crate::native_value::MaterializationReason::UnknownCallEscape,
                 );
             }
+            // #5247: under `--debug-symbols`, record this call's source byte
+            // offset so the dynamic method-dispatch emission site can emit a
+            // `js_set_call_location` immediately before the throwing dispatch
+            // (after the call's args — which may be nested calls that overwrite
+            // this — have been lowered). The dynamic dispatch path renders it as
+            // `at <file>:<line>` in the "X is not a function" TypeError's
+            // `.stack`. No-op in the default build.
+            if ctx.strings.debug_locations_enabled() {
+                ctx.strings.set_pending_call_offset(*byte_offset);
+            }
             lower_call(ctx, callee, args)
         }
 
diff --git a/crates/perry-codegen/src/expr/mod.rs b/crates/perry-codegen/src/expr/mod.rs
index 3984656516..4e7dc0ae1d 100644
--- a/crates/perry-codegen/src/expr/mod.rs
+++ b/crates/perry-codegen/src/expr/mod.rs
@@ -1402,7 +1402,7 @@ mod arrays_finds;
 mod bigint_set;
 mod binary;
 mod call_spread;
-mod calls;
+pub(crate) mod calls;
 mod child_proc;
 mod closure;
 mod compare;
diff --git a/crates/perry-codegen/src/expr/proxy_reflect.rs b/crates/perry-codegen/src/expr/proxy_reflect.rs
index 124a9642c3..7d62a0eb87 100644
--- a/crates/perry-codegen/src/expr/proxy_reflect.rs
+++ b/crates/perry-codegen/src/expr/proxy_reflect.rs
@@ -261,11 +261,13 @@ fn same_put_value_receiver_expr(target: &Expr, receiver: &Expr) -> bool {
                 callee: a_callee,
                 args: a_args,
                 type_args: a_type_args,
+                ..
             },
             Expr::Call {
                 callee: b_callee,
                 args: b_args,
                 type_args: b_type_args,
+                ..
             },
         ) => {
             a_type_args == b_type_args
diff --git a/crates/perry-codegen/src/lower_call/console_promise.rs b/crates/perry-codegen/src/lower_call/console_promise.rs
index 5fc49ee118..79e8dd243a 100644
--- a/crates/perry-codegen/src/lower_call/console_promise.rs
+++ b/crates/perry-codegen/src/lower_call/console_promise.rs
@@ -638,6 +638,11 @@ pub fn try_lower_native_method_str_dispatch(
     callee: &Expr,
     args: &[Expr],
 ) -> Result<Option<String>> {
+    // #5247: capture this call's source byte offset before any argument
+    // (possibly a nested call that overwrites the shared pending offset) is
+    // lowered, so the dynamic dispatch below can emit `js_set_call_location`
+    // with the OUTER call's location right before the throw-capable dispatch.
+    let call_byte_offset = ctx.strings.pending_call_offset();
     // -------- PropertyGet method dispatch via js_native_call_method --------
     //
     // For `recv.method(args)` where the static dispatch above didn't fire
@@ -788,6 +793,11 @@ pub fn try_lower_native_method_str_dispatch(
                 property,
                 TypedFeedbackContract::method_call(),
             );
+            // #5247: record the source location right before the dynamic
+            // dispatch so a thrown "X is not a function" TypeError carries
+            // `at <file>:<line>`. Args are already lowered above, so a nested
+            // call's location no longer shadows this one.
+            crate::expr::calls::emit_call_location_at(ctx, call_byte_offset);
             let blk = ctx.block();
             return Ok(Some(blk.call(
                 DOUBLE,
diff --git a/crates/perry-codegen/src/lower_call/property_get.rs b/crates/perry-codegen/src/lower_call/property_get.rs
index dc36fdad3c..528281f02d 100644
--- a/crates/perry-codegen/src/lower_call/property_get.rs
+++ b/crates/perry-codegen/src/lower_call/property_get.rs
@@ -93,6 +93,12 @@ pub fn try_lower_property_get_method_call(
     let Expr::PropertyGet { object, property } = callee else {
         return Ok(None);
     };
+    // #5247: capture this call's source byte offset now, before any argument
+    // (which may be a nested call that overwrites the pending offset) is
+    // lowered. The dynamic `js_native_call_method` fallback below emits the
+    // `js_set_call_location` from this captured value, immediately before the
+    // throwing dispatch. `0` (and the default build) → no emission.
+    let call_byte_offset = ctx.strings.pending_call_offset();
     if let Some(value) =
         super::web_storage::try_lower_web_storage_method_call(ctx, object, property, args)?
     {
@@ -1753,6 +1759,12 @@ pub fn try_lower_property_get_method_call(
                 ));
                 (ptr_reg, n.to_string())
             };
+            // #5247: record the source location of this call right before the
+            // dynamic dispatch, so the runtime "X is not a function" /
+            // "(kind).method is not a function" TypeError this fallback may
+            // throw carries `at <file>:<line>`. Args are already lowered, so a
+            // nested-call argument's location no longer shadows this one.
+            crate::expr::calls::emit_call_location_at(ctx, call_byte_offset);
             let v_def = ctx.block().call(
                 DOUBLE,
                 "js_native_call_method",
diff --git a/crates/perry-codegen/src/runtime_decls/strings_part2.rs b/crates/perry-codegen/src/runtime_decls/strings_part2.rs
index b9d072edd8..0bbbb818e6 100644
--- a/crates/perry-codegen/src/runtime_decls/strings_part2.rs
+++ b/crates/perry-codegen/src/runtime_decls/strings_part2.rs
@@ -406,6 +406,9 @@ pub(crate) fn declare_phase_b_strings_part2(module: &mut LlModule) {
     // `TypeError [ERR_INVALID_ARG_TYPE]` instead of dereferencing a bogus
     // pointer (segfault). Used by `crypto.createHash`/`createHmac`/`pbkdf2*`.
     module.declare_function("js_runtime_validate_string_arg", VOID, &[DOUBLE, PTR, I32]);
+    // #5247: source-location tracking for the dynamic call-dispatch throw
+    // path. Emitted before a call's dispatch only under `--debug-symbols`.
+    module.declare_function("js_set_call_location", VOID, &[PTR, I64, I32]);
     module.declare_function(
         "js_runtime_validate_crypto_key_arg",
         VOID,
diff --git a/crates/perry-codegen/src/strings.rs b/crates/perry-codegen/src/strings.rs
index d02f70fd6a..df90231e9c 100644
--- a/crates/perry-codegen/src/strings.rs
+++ b/crates/perry-codegen/src/strings.rs
@@ -76,6 +76,20 @@ pub struct StringPool {
     /// Ordered list of unique entries; the index in this Vec is the
     /// interned index referenced by `interned`.
     entries: Vec<StringEntry>,
+    /// #5247: source-location context for the dynamic call-dispatch throw
+    /// path. Set once per module after construction (only when the CLI
+    /// `--debug-symbols` flag is on). `None` in the default build so codegen
+    /// emits no per-call `js_set_call_location` overhead. When `Some`,
+    /// carries `(module_file_path, module_source)` so the call-lowering site
+    /// can resolve a `Call.byte_offset` to a `file:line`.
+    debug_location_ctx: Option<(String, String)>,
+    /// #5247: the byte offset of the `Expr::Call` currently being lowered,
+    /// recorded by the call dispatcher and consumed at the dynamic
+    /// method-dispatch emission site (after the call's arguments — which may
+    /// themselves be nested calls that overwrite this — have been lowered) so
+    /// the `js_set_call_location` is emitted with the *outer* call's offset
+    /// immediately before the throwing dispatch. `0` = none.
+    pending_call_offset: std::cell::Cell<u32>,
 }
 
 pub struct StringEntry {
@@ -107,6 +121,8 @@ impl StringPool {
             module_prefix,
             interned: HashMap::new(),
             entries: Vec::new(),
+            debug_location_ctx: None,
+            pending_call_offset: std::cell::Cell::new(0),
         }
     }
 
@@ -114,6 +130,53 @@ impl StringPool {
         &self.module_prefix
     }
 
+    /// #5247: install the per-module source-location context (file path +
+    /// source text) consulted by the dynamic call-dispatch lowering when the
+    /// `--debug-symbols` flag is on. No-op otherwise (`ctx` is `None`).
+    pub fn set_debug_location_ctx(&mut self, ctx: Option<(String, String)>) {
+        self.debug_location_ctx = ctx;
+    }
+
+    /// #5247: true iff source-location tracking is active for this module
+    /// (i.e. `--debug-symbols` installed a debug-location context). Lets the
+    /// dispatch emission site skip all location work in the default build.
+    pub fn debug_locations_enabled(&self) -> bool {
+        self.debug_location_ctx.is_some()
+    }
+
+    /// #5247: record the byte offset of the call currently being lowered.
+    pub fn set_pending_call_offset(&self, byte_offset: u32) {
+        self.pending_call_offset.set(byte_offset);
+    }
+
+    /// #5247: the byte offset recorded by the most recent
+    /// [`set_pending_call_offset`]. `0` when none.
+    pub fn pending_call_offset(&self) -> u32 {
+        self.pending_call_offset.get()
+    }
+
+    /// #5247: resolve a `Call`'s source byte offset to `(file_path, line)`,
+    /// where `line` is 1-based. Returns `None` when no debug-location context
+    /// is installed (default build), the offset is `0` (synthesized call), or
+    /// the offset is out of range. SWC's `BytePos` is 1-based, matching the
+    /// `lower` crate's `current_module_source_slice`, so subtract 1.
+    pub fn call_location_for(&self, byte_offset: u32) -> Option<(&str, u32)> {
+        if byte_offset == 0 {
+            return None;
+        }
+        let (file, src) = self.debug_location_ctx.as_ref()?;
+        let offset = (byte_offset.saturating_sub(1)) as usize;
+        if offset > src.len() {
+            return None;
+        }
+        // 1-based line = 1 + count of newlines before the offset.
+        let line = 1 + src.as_bytes()[..offset]
+            .iter()
+            .filter(|&&b| b == b'\n')
+            .count();
+        Some((file.as_str(), line as u32))
+    }
+
     /// Intern a string literal. Returns the interned index, stable for the
     /// life of the pool. Identical strings collapse to the same index.
     pub fn intern(&mut self, value: &str) -> u32 {
@@ -276,4 +339,78 @@ mod tests {
         let e = pool.entry(idx);
         assert_eq!(e.byte_len, 6);
     }
+
+    // ───────────────────── #5247 byte→line mapping ─────────────────────
+    // `call_location_for` takes an SWC `BytePos` (1-based), so byte offset N
+    // refers to source index N-1. Line is 1-based (1 + newlines before it).
+
+    fn pool_with_src(src: &str) -> StringPool {
+        let mut p = StringPool::new();
+        p.set_debug_location_ctx(Some(("foo.ts".to_string(), src.to_string())));
+        p
+    }
+
+    #[test]
+    fn call_location_none_without_debug_context() {
+        // Default build: no context installed → never resolves a location.
+        let p = StringPool::new();
+        assert_eq!(p.call_location_for(5), None);
+    }
+
+    #[test]
+    fn call_location_zero_offset_is_none() {
+        // 0 sentinel (synthesized call) → no location.
+        let p = pool_with_src("a\nb\nc");
+        assert_eq!(p.call_location_for(0), None);
+    }
+
+    #[test]
+    fn call_location_first_line() {
+        // Offsets within the first line (before any '\n') → line 1.
+        let p = pool_with_src("foo();\nbar();\n");
+        // BytePos 1 = source index 0 ('f'); BytePos 6 = index 5 (')').
+        assert_eq!(p.call_location_for(1), Some(("foo.ts", 1)));
+        assert_eq!(p.call_location_for(6), Some(("foo.ts", 1)));
+    }
+
+    #[test]
+    fn call_location_line_boundaries() {
+        // "foo();\nbar();\nbaz();\n"
+        //  index:0..5  '\n'=6  7..12 '\n'=13  14..19 '\n'=20
+        let src = "foo();\nbar();\nbaz();\n";
+        let p = pool_with_src(src);
+        // BytePos for the '\n' itself (index 6 → BytePos 7) still counts as
+        // line 1 (no newline strictly *before* it).
+        assert_eq!(p.call_location_for(7), Some(("foo.ts", 1)));
+        // First char of line 2 ('b' at index 7 → BytePos 8): one '\n' before.
+        assert_eq!(p.call_location_for(8), Some(("foo.ts", 2)));
+        // First char of line 3 ('b' at index 14 → BytePos 15): two '\n' before.
+        assert_eq!(p.call_location_for(15), Some(("foo.ts", 3)));
+    }
+
+    #[test]
+    fn call_location_last_line_and_out_of_range() {
+        let src = "x\ny\nz"; // 5 bytes, 3 lines, no trailing newline
+        let p = pool_with_src(src);
+        // 'z' at index 4 → BytePos 5: two '\n' before → line 3.
+        assert_eq!(p.call_location_for(5), Some(("foo.ts", 3)));
+        // BytePos == len+1 (index == len): clamped, still line 3 (EOF after z).
+        assert_eq!(p.call_location_for(6), Some(("foo.ts", 3)));
+        // Far out of range → None.
+        assert_eq!(p.call_location_for(100), None);
+    }
+
+    #[test]
+    fn call_location_utf8_safe() {
+        // Multi-byte chars before the call must not panic or miscount lines —
+        // we count raw bytes, and the offsets are byte offsets, so slicing on
+        // a byte boundary the compiler produced is always valid.
+        // "café();\nx();" — "café();" is 8 bytes (é = 2), '\n' at index 8.
+        let src = "café();\nx();";
+        let p = pool_with_src(src);
+        // 'x' is at byte index 9 (after "café();\n" = 9 bytes) → BytePos 10.
+        assert_eq!(p.call_location_for(10), Some(("foo.ts", 2)));
+        // A position inside line 1 → line 1.
+        assert_eq!(p.call_location_for(2), Some(("foo.ts", 1)));
+    }
 }
diff --git a/crates/perry-codegen/tests/class_keys_gc_root.rs b/crates/perry-codegen/tests/class_keys_gc_root.rs
index 2517f8394e..e62611395c 100644
--- a/crates/perry-codegen/tests/class_keys_gc_root.rs
+++ b/crates/perry-codegen/tests/class_keys_gc_root.rs
@@ -71,6 +71,8 @@ fn entry_opts() -> CompileOptions {
         deferred_module_prefixes: std::collections::HashSet::new(),
         module_init_deps: Vec::new(),
         is_dynamic_import_target: false,
+        debug_locations: false,
+        module_source: None,
     }
 }
 
diff --git a/crates/perry-codegen/tests/constructor_recursion.rs b/crates/perry-codegen/tests/constructor_recursion.rs
index 4bc8b3528c..56dc066296 100644
--- a/crates/perry-codegen/tests/constructor_recursion.rs
+++ b/crates/perry-codegen/tests/constructor_recursion.rs
@@ -47,6 +47,8 @@ fn empty_opts() -> CompileOptions {
         deferred_module_prefixes: std::collections::HashSet::new(),
         module_init_deps: Vec::new(),
         is_dynamic_import_target: false,
+        debug_locations: false,
+        module_source: None,
     }
 }
 
diff --git a/crates/perry-codegen/tests/large_object_barriers.rs b/crates/perry-codegen/tests/large_object_barriers.rs
index c032ebae3e..448ef45c7b 100644
--- a/crates/perry-codegen/tests/large_object_barriers.rs
+++ b/crates/perry-codegen/tests/large_object_barriers.rs
@@ -47,6 +47,8 @@ fn empty_opts() -> CompileOptions {
         deferred_module_prefixes: std::collections::HashSet::new(),
         module_init_deps: Vec::new(),
         is_dynamic_import_target: false,
+        debug_locations: false,
+        module_source: None,
     }
 }
 
diff --git a/crates/perry-codegen/tests/macos_bundle_chdir_gate.rs b/crates/perry-codegen/tests/macos_bundle_chdir_gate.rs
index c992a38a7b..5ff8acb1fd 100644
--- a/crates/perry-codegen/tests/macos_bundle_chdir_gate.rs
+++ b/crates/perry-codegen/tests/macos_bundle_chdir_gate.rs
@@ -53,6 +53,8 @@ fn entry_opts(target: Option<&str>) -> CompileOptions {
         deferred_module_prefixes: std::collections::HashSet::new(),
         module_init_deps: Vec::new(),
         is_dynamic_import_target: false,
+        debug_locations: false,
+        module_source: None,
     }
 }
 
diff --git a/crates/perry-codegen/tests/native_proof_buffer_views.rs b/crates/perry-codegen/tests/native_proof_buffer_views.rs
index 5de660a415..910495f6d1 100644
--- a/crates/perry-codegen/tests/native_proof_buffer_views.rs
+++ b/crates/perry-codegen/tests/native_proof_buffer_views.rs
@@ -52,6 +52,8 @@ fn empty_opts() -> CompileOptions {
         deferred_module_prefixes: std::collections::HashSet::new(),
         module_init_deps: Vec::new(),
         is_dynamic_import_target: false,
+        debug_locations: false,
+        module_source: None,
     }
 }
 
@@ -467,6 +469,7 @@ fn call(callee: Expr, args: Vec<Expr>) -> Expr {
         callee: Box::new(callee),
         args,
         type_args: Vec::new(),
+        byte_offset: 0,
     }
 }
 
@@ -590,6 +593,7 @@ fn artifact_records_buffer_read_u32_and_unsigned_materialization() {
             }),
             args: vec![int(0)],
             type_args: Vec::new(),
+            byte_offset: 0,
         })),
     ];
 
@@ -673,6 +677,7 @@ fn artifact_records_buffer_read_double_as_f64() {
             }),
             args: vec![int(0)],
             type_args: Vec::new(),
+            byte_offset: 0,
         })),
     ];
 
diff --git a/crates/perry-codegen/tests/native_proof_regressions.rs b/crates/perry-codegen/tests/native_proof_regressions.rs
index dadd995289..ea8a1a1553 100644
--- a/crates/perry-codegen/tests/native_proof_regressions.rs
+++ b/crates/perry-codegen/tests/native_proof_regressions.rs
@@ -52,6 +52,8 @@ fn empty_opts() -> CompileOptions {
         deferred_module_prefixes: std::collections::HashSet::new(),
         module_init_deps: Vec::new(),
         is_dynamic_import_target: false,
+        debug_locations: false,
+        module_source: None,
     }
 }
 
@@ -481,6 +483,7 @@ fn call(callee: Expr, args: Vec<Expr>) -> Expr {
         callee: Box::new(callee),
         args,
         type_args: Vec::new(),
+        byte_offset: 0,
     }
 }
 
@@ -829,11 +832,13 @@ fn pod_layout_specialization_module() -> Module {
         callee: Box::new(Expr::FuncRef(1)),
         args: vec![],
         type_args: vec![Type::Named("Tiny".to_string())],
+        byte_offset: 0,
     }));
     module.init.push(Stmt::Expr(Expr::Call {
         callee: Box::new(Expr::FuncRef(1)),
         args: vec![],
         type_args: vec![Type::Named("Wide".to_string())],
+        byte_offset: 0,
     }));
     module
 }
@@ -873,11 +878,13 @@ fn native_pod_view_specialization_module() -> Module {
         callee: Box::new(Expr::FuncRef(1)),
         args: vec![Expr::NativeArenaAlloc(Box::new(int(4096)))],
         type_args: vec![Type::Named("Tiny".to_string())],
+        byte_offset: 0,
     }));
     module.init.push(Stmt::Expr(Expr::Call {
         callee: Box::new(Expr::FuncRef(1)),
         args: vec![Expr::NativeArenaAlloc(Box::new(int(4096)))],
         type_args: vec![Type::Named("Wide".to_string())],
+        byte_offset: 0,
     }));
     module
 }
diff --git a/crates/perry-codegen/tests/shadow_slot_hygiene.rs b/crates/perry-codegen/tests/shadow_slot_hygiene.rs
index e9d54ddccb..56904988ec 100644
--- a/crates/perry-codegen/tests/shadow_slot_hygiene.rs
+++ b/crates/perry-codegen/tests/shadow_slot_hygiene.rs
@@ -47,6 +47,8 @@ fn empty_opts() -> CompileOptions {
         deferred_module_prefixes: std::collections::HashSet::new(),
         module_init_deps: Vec::new(),
         is_dynamic_import_target: false,
+        debug_locations: false,
+        module_source: None,
     }
 }
 
diff --git a/crates/perry-codegen/tests/static_symbol_hygiene.rs b/crates/perry-codegen/tests/static_symbol_hygiene.rs
index 0ae20f50b1..6eef851d69 100644
--- a/crates/perry-codegen/tests/static_symbol_hygiene.rs
+++ b/crates/perry-codegen/tests/static_symbol_hygiene.rs
@@ -47,6 +47,8 @@ fn empty_opts() -> CompileOptions {
         deferred_module_prefixes: std::collections::HashSet::new(),
         module_init_deps: Vec::new(),
         is_dynamic_import_target: false,
+        debug_locations: false,
+        module_source: None,
     }
 }
 
diff --git a/crates/perry-codegen/tests/typed_feedback.rs b/crates/perry-codegen/tests/typed_feedback.rs
index 93b7e109ac..063a7b7e6a 100644
--- a/crates/perry-codegen/tests/typed_feedback.rs
+++ b/crates/perry-codegen/tests/typed_feedback.rs
@@ -78,6 +78,8 @@ fn empty_opts() -> CompileOptions {
         deferred_module_prefixes: std::collections::HashSet::new(),
         module_init_deps: Vec::new(),
         is_dynamic_import_target: false,
+        debug_locations: false,
+        module_source: None,
     }
 }
 
@@ -238,6 +240,7 @@ fn typed_feedback_instruments_property_and_method_boundaries() {
                 }),
                 args: vec![Expr::Number(2.0)],
                 type_args: Vec::new(),
+                byte_offset: 0,
             }),
             Stmt::Return(Some(Expr::PropertyGet {
                 object: Box::new(Expr::LocalGet(1)),
@@ -328,6 +331,7 @@ fn typed_feedback_guards_direct_class_method_specialization() {
             }),
             args: vec![Expr::Number(5.0)],
             type_args: Vec::new(),
+            byte_offset: 0,
         }))],
     ));
 
@@ -377,6 +381,7 @@ fn typed_feedback_guards_direct_closure_call_specialization() {
                 callee: Box::new(Expr::LocalGet(2)),
                 args: vec![Expr::Number(9.0)],
                 type_args: Vec::new(),
+                byte_offset: 0,
             })),
         ],
     ));
diff --git a/crates/perry-codegen/tests/typed_shape_descriptor.rs b/crates/perry-codegen/tests/typed_shape_descriptor.rs
index 90d47b5c55..87d74b49d1 100644
--- a/crates/perry-codegen/tests/typed_shape_descriptor.rs
+++ b/crates/perry-codegen/tests/typed_shape_descriptor.rs
@@ -47,6 +47,8 @@ fn empty_opts() -> CompileOptions {
         deferred_module_prefixes: std::collections::HashSet::new(),
         module_init_deps: Vec::new(),
         is_dynamic_import_target: false,
+        debug_locations: false,
+        module_source: None,
     }
 }
 
diff --git a/crates/perry-codegen/tests/typed_shape_descriptors.rs b/crates/perry-codegen/tests/typed_shape_descriptors.rs
index 5b273a4d4b..aac9a8d048 100644
--- a/crates/perry-codegen/tests/typed_shape_descriptors.rs
+++ b/crates/perry-codegen/tests/typed_shape_descriptors.rs
@@ -77,6 +77,8 @@ fn empty_opts() -> CompileOptions {
         deferred_module_prefixes: std::collections::HashSet::new(),
         module_init_deps: Vec::new(),
         is_dynamic_import_target: false,
+        debug_locations: false,
+        module_source: None,
     }
 }
 
@@ -337,6 +339,7 @@ fn c262_array_has_own_property_uses_object_prototype_dispatch() {
                 }),
                 args: vec![Expr::String("0".to_string())],
                 type_args: vec![],
+                byte_offset: 0,
             })),
         ],
         Vec::new(),
diff --git a/crates/perry-hir/src/destructuring/assignment_stmt.rs b/crates/perry-hir/src/destructuring/assignment_stmt.rs
index 5c6b5a8565..4fd8c84200 100644
--- a/crates/perry-hir/src/destructuring/assignment_stmt.rs
+++ b/crates/perry-hir/src/destructuring/assignment_stmt.rs
@@ -38,6 +38,7 @@ fn extern_call(name: &str, args: Vec<Expr>) -> Expr {
         }),
         args,
         type_args: Vec::new(),
+        byte_offset: 0,
     }
 }
 
diff --git a/crates/perry-hir/src/dynamic_import/tests.rs b/crates/perry-hir/src/dynamic_import/tests.rs
index 1b5b34b089..e98db6c7eb 100644
--- a/crates/perry-hir/src/dynamic_import/tests.rs
+++ b/crates/perry-hir/src/dynamic_import/tests.rs
@@ -490,6 +490,7 @@ fn resolve_cjs_path_default_join_over_replaced_dirname_local() {
                 Expr::String("node_modules.asar.unpacked".to_string()),
             ],
             type_args: vec![],
+            byte_offset: 0,
         }),
     });
 
@@ -506,6 +507,7 @@ fn resolve_cjs_path_default_join_over_replaced_dirname_local() {
             Expr::String("worker/conoutSocketWorker.js".to_string()),
         ],
         type_args: vec![],
+        byte_offset: 0,
     };
 
     let consts = collect_module_const_locals(&module);
diff --git a/crates/perry-hir/src/ir/expr.rs b/crates/perry-hir/src/ir/expr.rs
index ba85f4e136..cff4e9af91 100644
--- a/crates/perry-hir/src/ir/expr.rs
+++ b/crates/perry-hir/src/ir/expr.rs
@@ -113,6 +113,13 @@ pub enum Expr {
         args: Vec<Expr>,
         /// Explicit type arguments (e.g., identity<number>(x))
         type_args: Vec<Type>,
+        /// #5247: byte offset (`call.span.lo.0`) of this call expression in its
+        /// module's source, captured at AST→HIR lowering. Used by codegen (under
+        /// `--debug-symbols`) to attach a `file:line` to the runtime "X is not a
+        /// function" TypeError thrown by the dynamic method-dispatch path. `0`
+        /// when unknown (synthesized calls from transforms/intrinsics, etc.) —
+        /// a 0 sentinel resolves to no location, falling back to `<anonymous>`.
+        byte_offset: u32,
     },
 
     /// Function call with spread arguments (e.g., fn(a, ...arr, b))
diff --git a/crates/perry-hir/src/jsx.rs b/crates/perry-hir/src/jsx.rs
index d82c389bea..bdd6fe1d41 100644
--- a/crates/perry-hir/src/jsx.rs
+++ b/crates/perry-hir/src/jsx.rs
@@ -89,6 +89,7 @@ pub(crate) fn lower_jsx_element(ctx: &mut LoweringContext, jsx: &ast::JSXElement
         }),
         args: vec![type_expr, props_expr],
         type_args: Vec::new(),
+        byte_offset: 0,
     })
 }
 
@@ -121,6 +122,7 @@ fn react_create_element_call(
         }),
         args: vec![type_expr, props_expr.clone()],
         type_args: Vec::new(),
+        byte_offset: 0,
     })
 }
 
@@ -189,6 +191,7 @@ pub(crate) fn lower_jsx_fragment(
         // `type === "__Fragment"` to detect fragment elements.
         args: vec![Expr::String("__Fragment".to_string()), props_expr],
         type_args: Vec::new(),
+        byte_offset: 0,
     })
 }
 
diff --git a/crates/perry-hir/src/lower/array_fold.rs b/crates/perry-hir/src/lower/array_fold.rs
index 2b09183430..f2f7f789b1 100644
--- a/crates/perry-hir/src/lower/array_fold.rs
+++ b/crates/perry-hir/src/lower/array_fold.rs
@@ -32,6 +32,7 @@ pub(crate) fn try_fold_array_method_call(call: Expr) -> Expr {
                 callee: Box::new(other),
                 args,
                 type_args: Vec::new(),
+                byte_offset: 0,
             };
         }
     };
@@ -43,6 +44,7 @@ pub(crate) fn try_fold_array_method_call(call: Expr) -> Expr {
         }),
         args,
         type_args: Vec::new(),
+        byte_offset: 0,
     };
     match property.as_str() {
         "map" if !args.is_empty() => {
diff --git a/crates/perry-hir/src/lower/const_fold_fn.rs b/crates/perry-hir/src/lower/const_fold_fn.rs
index df66c7aacb..157162b2ef 100644
--- a/crates/perry-hir/src/lower/const_fold_fn.rs
+++ b/crates/perry-hir/src/lower/const_fold_fn.rs
@@ -1449,5 +1449,6 @@ fn build_eval_completion_iife(
         callee: Box::new(closure),
         args: vec![],
         type_args: vec![],
+        byte_offset: 0,
     }))
 }
diff --git a/crates/perry-hir/src/lower/decorators.rs b/crates/perry-hir/src/lower/decorators.rs
index b89c61c5d9..379ba1f52b 100644
--- a/crates/perry-hir/src/lower/decorators.rs
+++ b/crates/perry-hir/src/lower/decorators.rs
@@ -176,6 +176,7 @@ fn append_method_decorator_init(
                 Expr::String(method.name.clone()),
             ],
             type_args: Vec::new(),
+            byte_offset: 0,
         },
     )]);
     append_decorator_invocations(
@@ -247,6 +248,7 @@ fn append_decorator_invocations_inner(
                     callee: Box::new(base),
                     args: dec.args.clone(),
                     type_args: Vec::new(),
+                    byte_offset: 0,
                 }),
             });
             callees.push((Expr::LocalGet(temp_id), dec.name.clone()));
@@ -260,6 +262,7 @@ fn append_decorator_invocations_inner(
             callee: Box::new(callee),
             args: invocation_args.clone(),
             type_args: Vec::new(),
+            byte_offset: 0,
         };
         match class_name_for_replacement_check {
             Some(class_name) => {
diff --git a/crates/perry-hir/src/lower/eval_super_scan.rs b/crates/perry-hir/src/lower/eval_super_scan.rs
index e13cd3e46a..fe8a163f00 100644
--- a/crates/perry-hir/src/lower/eval_super_scan.rs
+++ b/crates/perry-hir/src/lower/eval_super_scan.rs
@@ -146,6 +146,7 @@ fn throw_eval_syntax_error_expr(msg: &str) -> Expr {
         }),
         args: vec![Expr::String(msg.to_string())],
         type_args: vec![],
+        byte_offset: 0,
     }
 }
 
diff --git a/crates/perry-hir/src/lower/expr_assign.rs b/crates/perry-hir/src/lower/expr_assign.rs
index fb7f1d1a9f..40ddb11537 100644
--- a/crates/perry-hir/src/lower/expr_assign.rs
+++ b/crates/perry-hir/src/lower/expr_assign.rs
@@ -76,6 +76,7 @@ fn throw_type_error_const_assignment(name: &str) -> Expr {
         }),
         args: vec![Expr::String(name.to_string())],
         type_args: vec![],
+        byte_offset: 0,
     }
 }
 
@@ -88,6 +89,7 @@ fn throw_restricted_function_property_assignment() -> Expr {
         }),
         args: vec![],
         type_args: vec![],
+        byte_offset: 0,
     }
 }
 
@@ -100,6 +102,7 @@ fn throw_reference_error_unresolvable_assignment(name: &str) -> Expr {
         }),
         args: vec![Expr::String(name.to_string())],
         type_args: vec![],
+        byte_offset: 0,
     }
 }
 
@@ -547,6 +550,7 @@ fn lower_assignment_target(
                                 }),
                                 args: vec![*value],
                                 type_args: vec![],
+                                byte_offset: 0,
                             });
                         }
                     }
diff --git a/crates/perry-hir/src/lower/expr_call/crypto.rs b/crates/perry-hir/src/lower/expr_call/crypto.rs
index df50c9004e..89d269778f 100644
--- a/crates/perry-hir/src/lower/expr_call/crypto.rs
+++ b/crates/perry-hir/src/lower/expr_call/crypto.rs
@@ -124,6 +124,7 @@ pub(super) fn lower_crypto_passthrough(method: &str, args: Vec<Expr>) -> Option<
             }),
             args,
             type_args: vec![],
+            byte_offset: 0,
         }),
         // `randomUUIDv7([options])` — options accepted for shape parity but
         // do not affect the generated value (#2550).
@@ -145,6 +146,7 @@ pub(super) fn lower_crypto_passthrough(method: &str, args: Vec<Expr>) -> Option<
                     }),
                     args,
                     type_args: vec![],
+                    byte_offset: 0,
                 });
             }
             Some(Expr::CryptoRandomBytes(Box::new(
@@ -210,6 +212,7 @@ pub(super) fn lower_crypto_passthrough(method: &str, args: Vec<Expr>) -> Option<
             }),
             args,
             type_args: vec![],
+            byte_offset: 0,
         }),
         // `crypto.hash(alg, data, enc?)` — Node 21+ one-shot helper.
         // Expand into the `createHash(alg).update(data).digest(enc)`
@@ -234,16 +237,19 @@ pub(super) fn lower_crypto_passthrough(method: &str, args: Vec<Expr>) -> Option<
                                 }),
                                 args: vec![alg],
                                 type_args: vec![],
+                                byte_offset: 0,
                             }),
                             property: "update".to_string(),
                         }),
                         args: vec![data],
                         type_args: vec![],
+                        byte_offset: 0,
                     }),
                     property: "digest".to_string(),
                 }),
                 args: vec![enc],
                 type_args: vec![],
+                byte_offset: 0,
             })
         }
         _ => None,
diff --git a/crates/perry-hir/src/lower/expr_call/globals.rs b/crates/perry-hir/src/lower/expr_call/globals.rs
index d86779654b..47798c1f37 100644
--- a/crates/perry-hir/src/lower/expr_call/globals.rs
+++ b/crates/perry-hir/src/lower/expr_call/globals.rs
@@ -823,6 +823,7 @@ pub(super) fn try_global_builtins(
                                 }),
                                 args: new_args,
                                 type_args: vec![],
+                                byte_offset: 0,
                             }));
                         }
                     }
@@ -844,6 +845,7 @@ pub(super) fn try_global_builtins(
                                 }),
                                 args: vec![alg_arg, options_arg],
                                 type_args: vec![],
+                                byte_offset: 0,
                             }));
                         }
                     }
diff --git a/crates/perry-hir/src/lower/expr_call/intrinsics.rs b/crates/perry-hir/src/lower/expr_call/intrinsics.rs
index 2cbca78816..45901aad41 100644
--- a/crates/perry-hir/src/lower/expr_call/intrinsics.rs
+++ b/crates/perry-hir/src/lower/expr_call/intrinsics.rs
@@ -225,6 +225,7 @@ pub(super) fn try_strict_eval_arguments_assignment(
         }),
         args: Vec::new(),
         type_args: Vec::new(),
+        byte_offset: 0,
     })
 }
 
@@ -1317,6 +1318,7 @@ pub(super) fn try_iife_call_rewrite(
                                         callee: Box::new(lowered_callee),
                                         args: rest_args,
                                         type_args: Vec::new(),
+                                        byte_offset: 0,
                                     }));
                                 }
                             }
@@ -1441,6 +1443,7 @@ pub(super) fn try_native_module_method_apply_call(
                     }),
                     args: lowered,
                     type_args: Vec::new(),
+                    byte_offset: 0,
                 }));
             }
         }
diff --git a/crates/perry-hir/src/lower/expr_call/mod.rs b/crates/perry-hir/src/lower/expr_call/mod.rs
index 97bb2d5cb9..8a4f73ef30 100644
--- a/crates/perry-hir/src/lower/expr_call/mod.rs
+++ b/crates/perry-hir/src/lower/expr_call/mod.rs
@@ -633,6 +633,10 @@ fn lower_call_inner(ctx: &mut LoweringContext, call: &ast::CallExpr) -> Result<E
                     callee,
                     args,
                     type_args,
+                    // #5247: capture the call's source byte offset (same source as
+                    // DynamicImport's `byte_offset` below). Codegen resolves it to a
+                    // `file:line` for the runtime "X is not a function" TypeError.
+                    byte_offset: call.span.lo.0,
                 })
             }
         }
diff --git a/crates/perry-hir/src/lower/expr_call/module_class_static.rs b/crates/perry-hir/src/lower/expr_call/module_class_static.rs
index 6a4701b8c1..05efa743ff 100644
--- a/crates/perry-hir/src/lower/expr_call/module_class_static.rs
+++ b/crates/perry-hir/src/lower/expr_call/module_class_static.rs
@@ -172,6 +172,7 @@ pub(super) fn try_module_class_static(
                                         }),
                                         args: call_args,
                                         type_args: Vec::new(),
+                                        byte_offset: 0,
                                     }));
                                 }
                                 return Ok(Ok(Expr::NativeMethodCall {
diff --git a/crates/perry-hir/src/lower/expr_call/module_static.rs b/crates/perry-hir/src/lower/expr_call/module_static.rs
index 5979833195..b8a5631a38 100644
--- a/crates/perry-hir/src/lower/expr_call/module_static.rs
+++ b/crates/perry-hir/src/lower/expr_call/module_static.rs
@@ -1133,6 +1133,7 @@ pub(super) fn try_module_static_methods(
                                     }),
                                     args: vec![],
                                     type_args: vec![],
+                                    byte_offset: 0,
                                 }));
                             }
                         }
@@ -1343,6 +1344,7 @@ pub(super) fn try_module_static_methods(
                                     }),
                                     args: vec![b],
                                     type_args: vec![],
+                                    byte_offset: 0,
                                 }));
                             }
                         }
diff --git a/crates/perry-hir/src/lower/expr_call/native_module.rs b/crates/perry-hir/src/lower/expr_call/native_module.rs
index 029231a87b..aa972309c0 100644
--- a/crates/perry-hir/src/lower/expr_call/native_module.rs
+++ b/crates/perry-hir/src/lower/expr_call/native_module.rs
@@ -694,6 +694,7 @@ pub(super) fn try_native_module_methods(
                                     }),
                                     args: vec![b],
                                     type_args: vec![],
+                                    byte_offset: 0,
                                 }));
                             }
                         }
@@ -1472,6 +1473,7 @@ pub(super) fn try_native_module_methods(
                                 }),
                                 args: Vec::new(),
                                 type_args: Vec::new(),
+                                byte_offset: 0,
                             });
                             return Ok(Ok(Expr::Sequence(exprs)));
                         }
@@ -1516,6 +1518,7 @@ pub(super) fn try_native_module_methods(
                                     }),
                                     args: call_args,
                                     type_args: Vec::new(),
+                                    byte_offset: 0,
                                 }));
                             }
                         }
diff --git a/crates/perry-hir/src/lower/expr_call/post_args_dispatch.rs b/crates/perry-hir/src/lower/expr_call/post_args_dispatch.rs
index bb7a9da45b..d3094908ba 100644
--- a/crates/perry-hir/src/lower/expr_call/post_args_dispatch.rs
+++ b/crates/perry-hir/src/lower/expr_call/post_args_dispatch.rs
@@ -169,6 +169,7 @@ pub(super) fn try_object_has_own_call(
                                         }),
                                         args,
                                         type_args: Vec::new(),
+                                        byte_offset: 0,
                                     });
                                 }
                             }
@@ -205,6 +206,7 @@ pub(super) fn try_direct_has_own_call(
                         }),
                         args: vec![receiver, args[0].clone()],
                         type_args: Vec::new(),
+                        byte_offset: 0,
                     });
                 }
             }
@@ -270,6 +272,7 @@ pub(super) fn try_object_prototype_call(
                                             }),
                                             args,
                                             type_args: Vec::new(),
+                                            byte_offset: 0,
                                         });
                                     }
                                 }
diff --git a/crates/perry-hir/src/lower/expr_call/url_date_instance.rs b/crates/perry-hir/src/lower/expr_call/url_date_instance.rs
index ebf2536307..6755a3fbf1 100644
--- a/crates/perry-hir/src/lower/expr_call/url_date_instance.rs
+++ b/crates/perry-hir/src/lower/expr_call/url_date_instance.rs
@@ -181,6 +181,7 @@ pub(super) fn try_url_date_weakref_instance(
                         }),
                         args,
                         type_args: vec![],
+                        byte_offset: 0,
                     }));
                 }
                 cached_recv = Some(recv_expr);
@@ -481,6 +482,7 @@ pub(super) fn try_url_date_weakref_instance(
                         }),
                         args,
                         type_args: Vec::new(),
+                        byte_offset: 0,
                     }
                 };
                 if ctx.weakmap_locals.contains(&recv_name) {
diff --git a/crates/perry-hir/src/lower/expr_function.rs b/crates/perry-hir/src/lower/expr_function.rs
index ff350dc2a6..2a9262eace 100644
--- a/crates/perry-hir/src/lower/expr_function.rs
+++ b/crates/perry-hir/src/lower/expr_function.rs
@@ -554,6 +554,7 @@ fn lower_named_fn_expr(
         }),
         args: Vec::new(),
         type_args: Vec::new(),
+        byte_offset: 0,
     })
 }
 
diff --git a/crates/perry-hir/src/lower/expr_member.rs b/crates/perry-hir/src/lower/expr_member.rs
index cb758eaf68..793f8e2472 100644
--- a/crates/perry-hir/src/lower/expr_member.rs
+++ b/crates/perry-hir/src/lower/expr_member.rs
@@ -443,6 +443,7 @@ fn lower_member_inner(ctx: &mut LoweringContext, member: &ast::MemberExpr) -> Re
                             }),
                             args: vec![],
                             type_args: vec![],
+                            byte_offset: 0,
                         });
                     }
                     _ => {}
@@ -579,6 +580,7 @@ fn lower_member_inner(ctx: &mut LoweringContext, member: &ast::MemberExpr) -> Re
                             }),
                             args: vec![],
                             type_args: vec![],
+                            byte_offset: 0,
                         });
                     }
                     "on"
@@ -2486,6 +2488,7 @@ fn lower_member_inner(ctx: &mut LoweringContext, member: &ast::MemberExpr) -> Re
                     }),
                     args: vec![*index],
                     type_args: Vec::new(),
+                    byte_offset: 0,
                 });
             }
             Ok(Expr::IndexGet { object, index })
diff --git a/crates/perry-hir/src/lower/expr_misc.rs b/crates/perry-hir/src/lower/expr_misc.rs
index 697c55d9c7..63ece74885 100644
--- a/crates/perry-hir/src/lower/expr_misc.rs
+++ b/crates/perry-hir/src/lower/expr_misc.rs
@@ -160,6 +160,7 @@ pub(super) fn lower_update(ctx: &mut LoweringContext, update: &ast::UpdateExpr)
                         Expr::Bool(update.prefix),
                     ],
                     type_args: vec![],
+                    byte_offset: 0,
                 });
             };
             let op = match update.op {
diff --git a/crates/perry-hir/src/lower/expr_new.rs b/crates/perry-hir/src/lower/expr_new.rs
index 450c864137..14e66e2756 100644
--- a/crates/perry-hir/src/lower/expr_new.rs
+++ b/crates/perry-hir/src/lower/expr_new.rs
@@ -88,6 +88,7 @@ fn nonconstructable_builtin_throw_expr(name: &str, mut args: Vec<Expr>) -> Expr
         }),
         args: Vec::new(),
         type_args: Vec::new(),
+        byte_offset: 0,
     };
 
     if args.is_empty() {
@@ -680,6 +681,7 @@ pub(super) fn lower_new(ctx: &mut LoweringContext, new_expr: &ast::NewExpr) -> R
                     }),
                     args: Vec::new(),
                     type_args: Vec::new(),
+                    byte_offset: 0,
                 });
                 return Ok(Expr::Sequence(exprs));
             }
@@ -953,6 +955,7 @@ pub(super) fn lower_new(ctx: &mut LoweringContext, new_expr: &ast::NewExpr) -> R
                     }),
                     args,
                     type_args: Vec::new(),
+                    byte_offset: 0,
                 });
             }
 
diff --git a/crates/perry-hir/src/lower/expr_object.rs b/crates/perry-hir/src/lower/expr_object.rs
index 06bfbf66b7..d7129e9dc8 100644
--- a/crates/perry-hir/src/lower/expr_object.rs
+++ b/crates/perry-hir/src/lower/expr_object.rs
@@ -967,6 +967,7 @@ pub(super) fn lower_object(ctx: &mut LoweringContext, obj: &ast::ObjectLit) -> R
             }),
             args,
             type_args: Vec::new(),
+            byte_offset: 0,
         };
         let mut body: Vec<Stmt> = Vec::with_capacity(ops.len() * 4 + 1);
         let mut inner_local_ids = vec![param_id];
@@ -1103,6 +1104,7 @@ pub(super) fn lower_object(ctx: &mut LoweringContext, obj: &ast::ObjectLit) -> R
             callee: Box::new(closure),
             args: vec![Expr::Object(Vec::new())],
             type_args: vec![],
+            byte_offset: 0,
         });
     }
     let mut props = Vec::new();
@@ -1246,6 +1248,7 @@ pub(super) fn lower_object(ctx: &mut LoweringContext, obj: &ast::ObjectLit) -> R
         }),
         args,
         type_args: Vec::new(),
+        byte_offset: 0,
     };
     for init in computed_post_init {
         match init {
@@ -1308,6 +1311,7 @@ pub(super) fn lower_object(ctx: &mut LoweringContext, obj: &ast::ObjectLit) -> R
                     }),
                     args: vec![Expr::LocalGet(param_id), key, closure],
                     type_args: Vec::new(),
+                    byte_offset: 0,
                 }));
             }
         }
@@ -1359,5 +1363,6 @@ pub(super) fn lower_object(ctx: &mut LoweringContext, obj: &ast::ObjectLit) -> R
         callee: Box::new(closure),
         args: vec![static_obj],
         type_args: vec![],
+        byte_offset: 0,
     })
 }
diff --git a/crates/perry-hir/src/lower/lower_expr.rs b/crates/perry-hir/src/lower/lower_expr.rs
index ee1c68cbc3..d94e8a2338 100644
--- a/crates/perry-hir/src/lower/lower_expr.rs
+++ b/crates/perry-hir/src/lower/lower_expr.rs
@@ -63,6 +63,7 @@ pub(crate) fn throw_reference_error_expr(helper_name: &str) -> Expr {
         }),
         args: Vec::new(),
         type_args: Vec::new(),
+        byte_offset: 0,
     }
 }
 
@@ -196,6 +197,7 @@ pub(crate) fn with_implicit_unset_let(id: LocalId, name: String) -> Stmt {
             }),
             args: vec![],
             type_args: vec![],
+            byte_offset: 0,
         }),
     }
 }
@@ -495,6 +497,7 @@ pub(crate) fn lower_expr(ctx: &mut LoweringContext, expr: &ast::Expr) -> Result<
                         }),
                         args: vec![Expr::LocalGet(id), Expr::String(n.clone())],
                         type_args: vec![],
+                        byte_offset: 0,
                     });
                 }
                 Ok(Expr::LocalGet(id))
@@ -598,6 +601,7 @@ pub(crate) fn lower_expr(ctx: &mut LoweringContext, expr: &ast::Expr) -> Result<
                         }),
                         args: vec![Expr::String(name.clone())],
                         type_args: Vec::new(),
+                        byte_offset: 0,
                     });
                 }
                 if !known_global {
@@ -1051,6 +1055,7 @@ pub(crate) fn lower_expr(ctx: &mut LoweringContext, expr: &ast::Expr) -> Result<
                             }),
                             args: vec![Expr::String(n.to_string())],
                             type_args: Vec::new(),
+                            byte_offset: 0,
                         })));
                     }
                 }
@@ -1890,6 +1895,7 @@ pub(crate) fn lower_expr(ctx: &mut LoweringContext, expr: &ast::Expr) -> Result<
                             callee: Box::new(fixed_callee.clone()),
                             args,
                             type_args: Vec::new(),
+                            byte_offset: 0,
                         };
                         // For `foo?.bar?.(args)` the function value (`bar` on the
                         // un-short-circuited receiver) must itself be null-checked
@@ -1952,6 +1958,7 @@ pub(crate) fn lower_expr(ctx: &mut LoweringContext, expr: &ast::Expr) -> Result<
                             callee: Box::new(callee_expr),
                             args,
                             type_args: Vec::new(),
+                            byte_offset: 0,
                         })
                     };
 
@@ -2120,6 +2127,7 @@ pub(crate) fn lower_expr(ctx: &mut LoweringContext, expr: &ast::Expr) -> Result<
                 callee: Box::new(callee),
                 args: call_args,
                 type_args: vec![],
+                byte_offset: 0,
             })
         }
         // Class expression used as a value (not in `new` context) —
@@ -2574,5 +2582,6 @@ pub(crate) fn try_desugar_reactive_text(
         callee: Box::new(outer_closure),
         args: vec![],
         type_args: vec![],
+        byte_offset: 0,
     }))
 }
diff --git a/crates/perry-hir/src/lower/stmt_loops.rs b/crates/perry-hir/src/lower/stmt_loops.rs
index a385492999..4738235691 100644
--- a/crates/perry-hir/src/lower/stmt_loops.rs
+++ b/crates/perry-hir/src/lower/stmt_loops.rs
@@ -243,6 +243,7 @@ fn async_iterator_method_call(iterable: Expr) -> Expr {
         }),
         args: vec![],
         type_args: vec![],
+        byte_offset: 0,
     }
 }
 
@@ -254,6 +255,7 @@ fn iterator_return_call(iter_id: LocalId, needs_await: bool) -> Expr {
         }),
         args: vec![],
         type_args: vec![],
+        byte_offset: 0,
     };
     if needs_await {
         Expr::Await(Box::new(call))
@@ -339,6 +341,7 @@ fn iterator_result_validated(call: Expr) -> Expr {
         }),
         args: vec![call],
         type_args: vec![],
+        byte_offset: 0,
     }
 }
 
@@ -351,6 +354,7 @@ pub(crate) fn iterator_next_call(iter_id: LocalId) -> Expr {
         }),
         args: vec![],
         type_args: vec![],
+        byte_offset: 0,
     })
 }
 
@@ -671,6 +675,7 @@ fn lower_runtime_for_await_iterator(
         }),
         args: vec![],
         type_args: vec![],
+        byte_offset: 0,
     };
     let next_call = Expr::Await(Box::new(raw_next_call));
     module.init.push(Stmt::Let {
@@ -865,6 +870,7 @@ pub(crate) fn lower_stmt_for_of(
                 callee: Box::new(Expr::FuncRef(iter_fn_id)),
                 args: vec![iter_expr],
                 type_args: vec![],
+                byte_offset: 0,
             }
         } else if is_filehandle_readlines_for_await || is_fs_dir_for_await {
             async_iterator_method_call(iter_expr)
@@ -876,6 +882,7 @@ pub(crate) fn lower_stmt_for_of(
                 }),
                 args: vec![],
                 type_args: vec![],
+                byte_offset: 0,
             }
         } else if is_readline_interface_for_await {
             // rl.iterator() -> readline async-iterator object; .next() then
@@ -915,6 +922,7 @@ pub(crate) fn lower_stmt_for_of(
             }),
             args: vec![],
             type_args: vec![],
+            byte_offset: 0,
         };
         let next_call = if needs_await {
             Expr::Await(Box::new(raw_next_call))
diff --git a/crates/perry-hir/src/lower/widget_decl.rs b/crates/perry-hir/src/lower/widget_decl.rs
index 750921f33a..e67b8d107c 100644
--- a/crates/perry-hir/src/lower/widget_decl.rs
+++ b/crates/perry-hir/src/lower/widget_decl.rs
@@ -276,6 +276,7 @@ pub(super) fn try_desugar_reactive_animate(
         callee: Box::new(outer_closure),
         args: vec![],
         type_args: vec![],
+        byte_offset: 0,
     }))
 }
 
diff --git a/crates/perry-hir/src/lower_decl/block.rs b/crates/perry-hir/src/lower_decl/block.rs
index 5bf5152c1e..c8afe0a7f9 100644
--- a/crates/perry-hir/src/lower_decl/block.rs
+++ b/crates/perry-hir/src/lower_decl/block.rs
@@ -1084,6 +1084,7 @@ pub fn lower_stmts_using_aware(
                         }),
                         args: vec![Expr::Bool(is_async)],
                         type_args: Vec::new(),
+                        byte_offset: 0,
                     };
                     result.push(Stmt::If {
                         condition: Expr::Logical {
@@ -1163,6 +1164,7 @@ pub fn lower_stmts_using_aware(
                     }),
                     args: Vec::new(),
                     type_args: Vec::new(),
+                    byte_offset: 0,
                 };
                 if is_async {
                     call_expr = Expr::Await(Box::new(call_expr));
diff --git a/crates/perry-hir/src/lower_decl/body_stmt.rs b/crates/perry-hir/src/lower_decl/body_stmt.rs
index 398f1b3d1b..5993e484ce 100644
--- a/crates/perry-hir/src/lower_decl/body_stmt.rs
+++ b/crates/perry-hir/src/lower_decl/body_stmt.rs
@@ -1025,6 +1025,7 @@ pub fn lower_body_stmt(ctx: &mut LoweringContext, stmt: &ast::Stmt) -> Result<Ve
                         callee: Box::new(Expr::FuncRef(iter_fn_id)),
                         args: vec![iter_expr_raw],
                         type_args: vec![],
+                        byte_offset: 0,
                     }
                 } else if is_filehandle_readlines_for_await || is_fs_dir_for_await {
                     async_iterator_method_call(iter_expr_raw)
@@ -1036,6 +1037,7 @@ pub fn lower_body_stmt(ctx: &mut LoweringContext, stmt: &ast::Stmt) -> Result<Ve
                         }),
                         args: vec![],
                         type_args: vec![],
+                        byte_offset: 0,
                     }
                 } else if is_readline_interface_for_await {
                     Expr::NativeMethodCall {
@@ -1069,6 +1071,7 @@ pub fn lower_body_stmt(ctx: &mut LoweringContext, stmt: &ast::Stmt) -> Result<Ve
                     }),
                     args: vec![],
                     type_args: vec![],
+                    byte_offset: 0,
                 };
                 let next_call = if needs_await {
                     Expr::Await(Box::new(raw_next_call))
diff --git a/crates/perry-hir/src/lower_decl/body_stmt/detect.rs b/crates/perry-hir/src/lower_decl/body_stmt/detect.rs
index 8e13d94edc..a09b903fbe 100644
--- a/crates/perry-hir/src/lower_decl/body_stmt/detect.rs
+++ b/crates/perry-hir/src/lower_decl/body_stmt/detect.rs
@@ -180,6 +180,7 @@ pub(super) fn iterator_return_call(iter_id: LocalId, needs_await: bool) -> Expr
         }),
         args: vec![],
         type_args: vec![],
+        byte_offset: 0,
     };
     if needs_await {
         Expr::Await(Box::new(call))
diff --git a/crates/perry-hir/src/lower_decl/body_stmt/for_await.rs b/crates/perry-hir/src/lower_decl/body_stmt/for_await.rs
index 5231abc2b3..2ffcc6bae3 100644
--- a/crates/perry-hir/src/lower_decl/body_stmt/for_await.rs
+++ b/crates/perry-hir/src/lower_decl/body_stmt/for_await.rs
@@ -29,6 +29,7 @@ pub(super) fn lower_runtime_for_await_iterator_body(
         }),
         args: vec![],
         type_args: vec![],
+        byte_offset: 0,
     };
     let next_call = Expr::Await(Box::new(raw_next_call));
     result.push(Stmt::Let {
diff --git a/crates/perry-hir/src/lower_decl/class_computed.rs b/crates/perry-hir/src/lower_decl/class_computed.rs
index c40dcdef16..3c1b7ee4ae 100644
--- a/crates/perry-hir/src/lower_decl/class_computed.rs
+++ b/crates/perry-hir/src/lower_decl/class_computed.rs
@@ -89,6 +89,7 @@ pub(crate) fn push_deduped_class_computed_keys(
                 }),
                 args: vec![lowered],
                 type_args: Vec::new(),
+                byte_offset: 0,
             }));
         }
     }
diff --git a/crates/perry-hir/src/lower_decl/class_decl.rs b/crates/perry-hir/src/lower_decl/class_decl.rs
index 70ea36c7d0..67fb6ed8ea 100644
--- a/crates/perry-hir/src/lower_decl/class_decl.rs
+++ b/crates/perry-hir/src/lower_decl/class_decl.rs
@@ -204,6 +204,7 @@ fn synthesize_symbol_iterator_wrapper(
             callee: Box::new(Expr::FuncRef(top_fn_id)),
             args: vec![Expr::This],
             type_args: Vec::new(),
+            byte_offset: 0,
         }))],
         is_async: false,
         is_generator: false,
diff --git a/crates/perry-hir/src/lower_decl/helpers.rs b/crates/perry-hir/src/lower_decl/helpers.rs
index 82f5ec60d9..d7ecc428aa 100644
--- a/crates/perry-hir/src/lower_decl/helpers.rs
+++ b/crates/perry-hir/src/lower_decl/helpers.rs
@@ -51,6 +51,7 @@ pub(super) fn async_iterator_method_call(iterable: Expr) -> Expr {
         }),
         args: vec![],
         type_args: vec![],
+        byte_offset: 0,
     }
 }
 
diff --git a/crates/perry-hir/src/monomorph/driver.rs b/crates/perry-hir/src/monomorph/driver.rs
index 639579b4aa..36e8fda847 100644
--- a/crates/perry-hir/src/monomorph/driver.rs
+++ b/crates/perry-hir/src/monomorph/driver.rs
@@ -217,6 +217,7 @@ fn collect_instantiations_in_expr(
             callee,
             args,
             type_args,
+            ..
         } => {
             // First collect in the callee and args
             collect_instantiations_in_expr(callee, ctx, module, idx);
diff --git a/crates/perry-hir/src/monomorph/substitute_expr.rs b/crates/perry-hir/src/monomorph/substitute_expr.rs
index fb8c87c810..fea3abf25f 100644
--- a/crates/perry-hir/src/monomorph/substitute_expr.rs
+++ b/crates/perry-hir/src/monomorph/substitute_expr.rs
@@ -55,6 +55,7 @@ pub(crate) fn substitute_expr(expr: &Expr, substitutions: &HashMap<String, Type>
             callee,
             args,
             type_args,
+            byte_offset,
         } => Expr::Call {
             callee: Box::new(substitute_expr(callee, substitutions)),
             args: args
@@ -65,6 +66,7 @@ pub(crate) fn substitute_expr(expr: &Expr, substitutions: &HashMap<String, Type>
                 .iter()
                 .map(|t| substitute_type(t, substitutions))
                 .collect(),
+            byte_offset: *byte_offset,
         },
         Expr::PodLayoutSizeOf { ty } => Expr::PodLayoutSizeOf {
             ty: substitute_type(ty, substitutions),
diff --git a/crates/perry-hir/src/monomorph/tests.rs b/crates/perry-hir/src/monomorph/tests.rs
index 8fb3d933ce..af7d09c7ef 100644
--- a/crates/perry-hir/src/monomorph/tests.rs
+++ b/crates/perry-hir/src/monomorph/tests.rs
@@ -83,6 +83,7 @@ fn test_monomorphize_substitutes_pod_layout_type_vars() {
         callee: Box::new(Expr::FuncRef(1)),
         args: vec![],
         type_args: vec![packet_ty.clone()],
+        byte_offset: 0,
     }));
 
     monomorphize_module(&mut module);
@@ -159,6 +160,7 @@ fn test_monomorphize_substitutes_native_pod_view_type_vars() {
         callee: Box::new(Expr::FuncRef(1)),
         args: vec![Expr::NativeArenaAlloc(Box::new(Expr::Integer(64)))],
         type_args: vec![packet_ty],
+        byte_offset: 0,
     }));
 
     monomorphize_module(&mut module);
@@ -218,6 +220,7 @@ fn test_monomorphize_generic_function() {
         callee: Box::new(Expr::FuncRef(1)),
         args: vec![Expr::Number(42.0)],
         type_args: vec![Type::Number],
+        byte_offset: 0,
     }));
 
     // Run monomorphization
@@ -294,6 +297,7 @@ fn test_monomorphize_updates_call_sites() {
         callee: Box::new(Expr::FuncRef(1)),
         args: vec![Expr::String("hello".to_string())],
         type_args: vec![Type::String],
+        byte_offset: 0,
     }));
 
     // Run monomorphization
@@ -336,11 +340,13 @@ fn test_monomorphize_updates_native_memory_copy_operand_generic_calls() {
             callee: Box::new(Expr::FuncRef(1)),
             args: vec![],
             type_args: vec![packet_ty.clone()],
+            byte_offset: 0,
         }),
         src: Box::new(Expr::Call {
             callee: Box::new(Expr::FuncRef(2)),
             args: vec![],
             type_args: vec![packet_ty],
+            byte_offset: 0,
         }),
     }));
 
@@ -369,11 +375,13 @@ fn test_monomorphize_updates_native_memory_fill_u32_operand_generic_calls() {
             callee: Box::new(Expr::FuncRef(1)),
             args: vec![],
             type_args: vec![packet_ty.clone()],
+            byte_offset: 0,
         }),
         value: Box::new(Expr::Call {
             callee: Box::new(Expr::FuncRef(2)),
             args: vec![],
             type_args: vec![packet_ty],
+            byte_offset: 0,
         }),
     }));
 
@@ -569,6 +577,7 @@ fn test_type_inference_from_arguments() {
         callee: Box::new(Expr::FuncRef(1)),
         args: vec![Expr::Number(42.0)],
         type_args: vec![], // Empty - should be inferred!
+        byte_offset: 0,
     }));
 
     // Run monomorphization
@@ -666,6 +675,7 @@ fn test_type_inference_string() {
         callee: Box::new(Expr::FuncRef(1)),
         args: vec![Expr::String("hello".to_string())],
         type_args: vec![], // Empty - should be inferred!
+        byte_offset: 0,
     }));
 
     // Run monomorphization
@@ -735,6 +745,7 @@ fn test_type_inference_rest_type_var_binds_tuple() {
             Expr::String("c".to_string()),
         ],
         type_args: vec![],
+        byte_offset: 0,
     }));
 
     monomorphize_module(&mut module);
@@ -789,6 +800,7 @@ fn test_type_inference_rest_array_binds_element_type() {
         callee: Box::new(Expr::FuncRef(1)),
         args: vec![Expr::String("a".to_string()), Expr::String("b".to_string())],
         type_args: vec![],
+        byte_offset: 0,
     }));
 
     monomorphize_module(&mut module);
@@ -892,6 +904,7 @@ fn generic_call(func_id: FuncId, ty: &Type) -> Expr {
         callee: Box::new(Expr::FuncRef(func_id)),
         args: vec![],
         type_args: vec![ty.clone()],
+        byte_offset: 0,
     }
 }
 
diff --git a/crates/perry-hir/src/monomorph/update_call_sites.rs b/crates/perry-hir/src/monomorph/update_call_sites.rs
index 5f8400dd44..3f0bb7f9f1 100644
--- a/crates/perry-hir/src/monomorph/update_call_sites.rs
+++ b/crates/perry-hir/src/monomorph/update_call_sites.rs
@@ -135,6 +135,7 @@ fn update_call_sites_in_expr(
             callee,
             args,
             type_args,
+            ..
         } => {
             // First update the callee and args recursively
             update_call_sites_in_expr(callee, ctx, lookup);
diff --git a/crates/perry-hir/src/stable_hash/expr.rs b/crates/perry-hir/src/stable_hash/expr.rs
index b708b1b108..2cd353a424 100644
--- a/crates/perry-hir/src/stable_hash/expr.rs
+++ b/crates/perry-hir/src/stable_hash/expr.rs
@@ -48,7 +48,11 @@ impl SH for Expr {
             Expr::Unary { op, operand } => { tag(h, 15); op.hash(h); operand.as_ref().hash(h); }
             Expr::Compare { op, left, right } => { tag(h, 16); op.hash(h); left.as_ref().hash(h); right.as_ref().hash(h); }
             Expr::Logical { op, left, right } => { tag(h, 17); op.hash(h); left.as_ref().hash(h); right.as_ref().hash(h); }
-            Expr::Call { callee, args, type_args, } => { tag(h, 18); callee.as_ref().hash(h); args.hash(h); type_args.hash(h); }
+            // #5247: `byte_offset` is diagnostic-only (source-location metadata
+            // for runtime TypeErrors); deliberately excluded from the stable hash
+            // so source whitespace edits that shift offsets don't bust the object
+            // cache.
+            Expr::Call { callee, args, type_args, .. } => { tag(h, 18); callee.as_ref().hash(h); args.hash(h); type_args.hash(h); }
             Expr::CallSpread { callee, args, type_args, } => { tag(h, 19); callee.as_ref().hash(h); args.hash(h); type_args.hash(h); }
             Expr::SuperCallSpread(args) => { tag(h, 12240); for a in args { match a { CallArg::Expr(e) | CallArg::Spread(e) => e.hash(h), } } }
             Expr::PodLayoutSizeOf { ty } => { tag(h, 12001); ty.hash(h); }
diff --git a/crates/perry-runtime/src/error.rs b/crates/perry-runtime/src/error.rs
index 35ed5ddd27..2ead024874 100644
--- a/crates/perry-runtime/src/error.rs
+++ b/crates/perry-runtime/src/error.rs
@@ -81,13 +81,65 @@ pub struct ErrorHeader {
     pub errors: *mut crate::array::ArrayHeader,
 }
 
+thread_local! {
+    /// #5247: the source location (`file`, 1-based `line`) of the call
+    /// currently being dispatched, set by codegen-emitted
+    /// `js_set_call_location` immediately before a dynamic method/call
+    /// dispatch that can throw "X is not a function" / "is not a
+    /// constructor". `make_stack` reads it so the thrown TypeError's
+    /// `.stack` shows `at <file>:<line>` instead of `at <anonymous>`.
+    ///
+    /// Only populated when the program was compiled with `--debug-symbols`
+    /// (the flag that gates the codegen emission). `None` in the default
+    /// build, so release perf and the `<anonymous>` fallback are unchanged.
+    static CURRENT_CALL_LOCATION: std::cell::RefCell<Option<(String, u32)>> =
+        const { std::cell::RefCell::new(None) };
+}
+
+/// #5247: record the source location of the call about to be dispatched.
+/// Codegen emits this call right before a dynamic dispatch under
+/// `--debug-symbols`. `file_ptr`/`file_len` are the (UTF-8) source path;
+/// `line` is the 1-based line number. A `line` of 0 clears the location.
+///
+/// # Safety
+/// `file_ptr` must point to `file_len` valid bytes, or be null with
+/// `file_len == 0`.
+#[no_mangle]
+pub unsafe extern "C" fn js_set_call_location(file_ptr: *const u8, file_len: usize, line: u32) {
+    if line == 0 || file_ptr.is_null() || file_len == 0 {
+        CURRENT_CALL_LOCATION.with(|c| *c.borrow_mut() = None);
+        return;
+    }
+    let bytes = std::slice::from_raw_parts(file_ptr, file_len);
+    let file = String::from_utf8_lossy(bytes).into_owned();
+    CURRENT_CALL_LOCATION.with(|c| *c.borrow_mut() = Some((file, line)));
+}
+
+// Generated-code-only callee: anchor against the auto-optimize LTO dead-strip
+// (see project_auto_optimize_keepalive_3320).
+#[used]
+static KEEP_JS_SET_CALL_LOCATION: unsafe extern "C" fn(*const u8, usize, u32) =
+    js_set_call_location;
+
+/// #5247: render the current call-location frame, or `<anonymous>` when no
+/// location was recorded (default builds, or a synthesized/offset-less site).
+fn current_stack_frame() -> String {
+    CURRENT_CALL_LOCATION.with(|c| match &*c.borrow() {
+        Some((file, line)) => format!("    at {}:{}", file, line),
+        None => "    at <anonymous>".to_string(),
+    })
+}
+
 unsafe fn make_stack(name: &str, message: &str) -> *mut StringHeader {
-    // Build a simple "<name>: <message>\n    at <anonymous>" string.
-    // Real stack traces are not implemented; the test only checks `.includes(message)`.
+    // Build a simple "<name>: <message>\n    at <file>:<line>" string
+    // (or "<anonymous>" when no #5247 source location is recorded). Real
+    // multi-frame stack traces are not implemented; the test only checks
+    // `.includes(message)`.
+    let frame = current_stack_frame();
     let s = if message.is_empty() {
-        format!("{}\n    at <anonymous>", name)
+        format!("{}\n{}", name, frame)
     } else {
-        format!("{}: {}\n    at <anonymous>", name, message)
+        format!("{}: {}\n{}", name, message, frame)
     };
     js_string_from_bytes(s.as_ptr(), s.len() as u32)
 }
diff --git a/crates/perry-transform/src/deforest/call_sites.rs b/crates/perry-transform/src/deforest/call_sites.rs
index d99c10c784..c4032398fb 100644
--- a/crates/perry-transform/src/deforest/call_sites.rs
+++ b/crates/perry-transform/src/deforest/call_sites.rs
@@ -211,6 +211,7 @@ fn try_consumer_fuse_pattern(
                     callee,
                     args,
                     type_args,
+                    ..
                 }),
             ..
         } => match callee.as_ref() {
@@ -253,6 +254,8 @@ fn try_consumer_fuse_pattern(
         callee: Box::new(Expr::FuncRef(callee_id)),
         args: new_args,
         type_args,
+        // #5247: deforestation-fused call; no single source offset.
+        byte_offset: 0,
     };
     Some((2, vec![Stmt::Expr(new_call)]))
 }
@@ -387,6 +390,7 @@ fn try_rewrite_single_stmt(
                     callee,
                     args,
                     type_args,
+                    ..
                 }),
         } => match callee.as_ref() {
             Expr::FuncRef(fid) if producers.contains_key(fid) => {
@@ -397,6 +401,7 @@ fn try_rewrite_single_stmt(
                     callee: callee.clone(),
                     args: new_args,
                     type_args: type_args.clone(),
+                    byte_offset: 0,
                 });
                 let let_stmt = Stmt::Let {
                     id: *id,
diff --git a/crates/perry-transform/src/deforest/tests.rs b/crates/perry-transform/src/deforest/tests.rs
index 1ca83d2d43..f7bd55ba67 100644
--- a/crates/perry-transform/src/deforest/tests.rs
+++ b/crates/perry-transform/src/deforest/tests.rs
@@ -58,6 +58,7 @@ fn rejects_producer_with_out_passed_to_call() {
         callee: Box::new(Expr::FuncRef(99)),
         args: vec![Expr::LocalGet(10)],
         type_args: vec![],
+        byte_offset: 0,
     });
     assert!(analyze_producer(&func).is_none());
 }
@@ -159,6 +160,7 @@ fn rejects_producer_called_inside_closure() {
                     callee: Box::new(Expr::FuncRef(1)),
                     args: vec![],
                     type_args: vec![],
+                    byte_offset: 0,
                 }),
             },
             // return v.length;
@@ -247,6 +249,7 @@ fn still_deforests_when_caller_is_not_a_closure() {
                 callee: Box::new(Expr::FuncRef(1)),
                 args: vec![],
                 type_args: vec![],
+                byte_offset: 0,
             }),
         }],
         is_async: false,
diff --git a/crates/perry-transform/src/generator/helpers.rs b/crates/perry-transform/src/generator/helpers.rs
index 299061ce8f..10c81b1024 100644
--- a/crates/perry-transform/src/generator/helpers.rs
+++ b/crates/perry-transform/src/generator/helpers.rs
@@ -107,6 +107,7 @@ pub fn wrap_in_promise_resolve(value: Expr) -> Expr {
         }),
         args: vec![value],
         type_args: vec![],
+        byte_offset: 0,
     }
 }
 
diff --git a/crates/perry-transform/src/generator/linearize.rs b/crates/perry-transform/src/generator/linearize.rs
index c4f30e9666..2a5d565d69 100644
--- a/crates/perry-transform/src/generator/linearize.rs
+++ b/crates/perry-transform/src/generator/linearize.rs
@@ -84,6 +84,7 @@ fn delegate_next_call(del_next_id: LocalId, del_iter_id: LocalId, arg: Expr) ->
             }),
             args: call_args,
             type_args: vec![],
+            byte_offset: 0,
         }),
         else_expr: Box::new(Expr::Call {
             callee: Box::new(Expr::PropertyGet {
@@ -92,6 +93,7 @@ fn delegate_next_call(del_next_id: LocalId, del_iter_id: LocalId, arg: Expr) ->
             }),
             args: method_args,
             type_args: vec![],
+            byte_offset: 0,
         }),
     }
 }
diff --git a/crates/perry-transform/src/generator/lower.rs b/crates/perry-transform/src/generator/lower.rs
index 8553e220a1..647f04986c 100644
--- a/crates/perry-transform/src/generator/lower.rs
+++ b/crates/perry-transform/src/generator/lower.rs
@@ -1075,6 +1075,7 @@ fn promise_reject(value: Expr) -> Expr {
         }),
         args: vec![value],
         type_args: vec![],
+        byte_offset: 0,
     }
 }
 
@@ -1889,6 +1890,7 @@ pub fn build_async_step_driver_direct(
         }),
         args: vec![arg],
         type_args: vec![],
+        byte_offset: 0,
     };
     let promise_reject = |arg: Expr| Expr::Call {
         callee: Box::new(Expr::PropertyGet {
@@ -1897,6 +1899,7 @@ pub fn build_async_step_driver_direct(
         }),
         args: vec![arg],
         type_args: vec![],
+        byte_offset: 0,
     };
 
     // Rewrite every Return inside next_body to LabeledBreak(__step_done)
@@ -1957,6 +1960,7 @@ pub fn build_async_step_driver_direct(
                 callee: Box::new(Expr::LocalGet(tid)),
                 args: vec![Expr::LocalGet(value_param_id)],
                 type_args: vec![],
+                byte_offset: 0,
             })]
         } else {
             // No __async_throw closure was constructed (callee passed None).
@@ -2033,6 +2037,7 @@ pub fn build_async_step_driver_direct(
                         callee: Box::new(Expr::LocalGet(step_self_id)),
                         args: vec![Expr::LocalGet(catch_e_id), Expr::Bool(true)],
                         type_args: vec![],
+                        byte_offset: 0,
                     })),
                 ],
             }),
diff --git a/crates/perry-transform/src/state_desugar.rs b/crates/perry-transform/src/state_desugar.rs
index 93328368b0..0b883868d3 100644
--- a/crates/perry-transform/src/state_desugar.rs
+++ b/crates/perry-transform/src/state_desugar.rs
@@ -907,6 +907,7 @@ fn try_rewrite_foreach(
         callee: Box::new(closure),
         args: vec![],
         type_args: vec![],
+        byte_offset: 0,
     })
 }
 
@@ -1103,6 +1104,7 @@ fn try_rewrite_navstack(
         callee: Box::new(closure),
         args: vec![],
         type_args: vec![],
+        byte_offset: 0,
     })
 }
 
diff --git a/crates/perry/src/commands/compile.rs b/crates/perry/src/commands/compile.rs
index ac7e6d4b07..a7a12b49c2 100644
--- a/crates/perry/src/commands/compile.rs
+++ b/crates/perry/src/commands/compile.rs
@@ -4031,6 +4031,17 @@ pub fn run_with_parse_cache(
                 // alone is insufficient because it's empty when the
                 // target has no `export` statements.
                 is_dynamic_import_target: dyn_target_paths.contains(path),
+                // #5247: source-location tracking for the dynamic call-dispatch
+                // throw path. Gated by `--debug-symbols` so the default build is
+                // unchanged (no source read, no per-call emission). When on, read
+                // the module's original source so codegen can map a Call's byte
+                // offset to a 1-based line.
+                debug_locations: args.debug_symbols,
+                module_source: if args.debug_symbols {
+                    std::fs::read_to_string(path).ok()
+                } else {
+                    None
+                },
             };
             // V2.2 + #686 object cache lookup. The key hashes every
             // codegen-affecting field of `opts` together with this
diff --git a/crates/perry/src/commands/compile/object_cache.rs b/crates/perry/src/commands/compile/object_cache.rs
index 7b4ef5d1f1..b10ba65c63 100644
--- a/crates/perry/src/commands/compile/object_cache.rs
+++ b/crates/perry/src/commands/compile/object_cache.rs
@@ -165,6 +165,11 @@ fn compute_object_cache_key_with_env(
     // doesn't usually move between rebuilds.
     h.field("build_id", &format!("{:016x}", perry_build_id()));
     h.field("ir_only", if opts.emit_ir_only { "1" } else { "0" });
+    // #5247: `--debug-symbols` flips per-call `js_set_call_location` emission,
+    // which changes the emitted IR (and `.o` bytes). Without this in the key,
+    // toggling the flag would serve the previously-cached object and the
+    // source locations would silently not appear.
+    h.field("dbgloc", if opts.debug_locations { "1" } else { "0" });
     h.field(
         "verify_native_regions",
         if opts.verify_native_regions { "1" } else { "0" },
@@ -948,6 +953,8 @@ mod object_cache_tests {
             deferred_module_prefixes: std::collections::HashSet::new(),
             module_init_deps: Vec::new(),
             is_dynamic_import_target: false,
+            debug_locations: false,
+            module_source: None,
         }
     }
 
@@ -1017,6 +1024,20 @@ mod object_cache_tests {
         );
     }
 
+    #[test]
+    fn key_changes_with_debug_locations_flag() {
+        // #5247: toggling --debug-symbols (debug_locations) flips per-call
+        // location emission, so cached objects must not be shared across it.
+        let mut a = empty_opts();
+        let mut b = empty_opts();
+        a.debug_locations = false;
+        b.debug_locations = true;
+        assert_ne!(
+            compute_object_cache_key(&a, 1, "0.5.156"),
+            compute_object_cache_key(&b, 1, "0.5.156")
+        );
+    }
+
     #[test]
     fn key_changes_with_fast_math_flag() {
         // Without this guard, `perry --fast-math foo.ts` after a default
diff --git a/crates/perry/tests/issue_5247_runtime_error_source_location.rs b/crates/perry/tests/issue_5247_runtime_error_source_location.rs
new file mode 100644
index 0000000000..bebb089b9f
--- /dev/null
+++ b/crates/perry/tests/issue_5247_runtime_error_source_location.rs
@@ -0,0 +1,158 @@
+//! Regression test for #5247 (first increment): runtime TypeErrors from the
+//! dynamic call-dispatch path ("X is not a function") carry a real source
+//! `file:line` in `.stack` / `.message`'s frame when the program is compiled
+//! with `--debug-symbols`.
+//!
+//! Behavior:
+//!   • WITH `--debug-symbols`: the thrown TypeError's `.stack` contains
+//!     `at <file>:<line>` pointing at the offending call's line.
+//!   • WITHOUT the flag (default build): unchanged — `at <anonymous>`.
+//!
+//! The fixture exercises the highest-value path the increment targets: a
+//! method call on an `any`-typed value that is actually a primitive at runtime
+//! (`const f: any = 5; f.test();`), which dispatches dynamically and throws
+//! `TypeError: (number).test is not a function`.
+
+use std::path::PathBuf;
+use std::process::Command;
+use std::sync::Once;
+
+fn perry_bin() -> PathBuf {
+    PathBuf::from(env!("CARGO_BIN_EXE_perry"))
+}
+
+fn workspace_root() -> PathBuf {
+    PathBuf::from(env!("CARGO_MANIFEST_DIR"))
+        .join("../..")
+        .canonicalize()
+        .expect("canonicalize workspace root")
+}
+
+fn target_debug_dir() -> PathBuf {
+    std::env::var_os("CARGO_TARGET_DIR")
+        .map(PathBuf::from)
+        .unwrap_or_else(|| workspace_root().join("target"))
+        .join("debug")
+}
+
+/// Build `libperry_runtime.a` once so the compiled binaries can link.
+fn ensure_runtime_archive() {
+    static BUILD_RUNTIME: Once = Once::new();
+    BUILD_RUNTIME.call_once(|| {
+        let cargo = std::env::var_os("CARGO").unwrap_or_else(|| "cargo".into());
+        let build = Command::new(cargo)
+            .current_dir(workspace_root())
+            .arg("build")
+            .arg("-p")
+            .arg("perry-runtime")
+            .output()
+            .expect("run cargo build -p perry-runtime");
+        assert!(
+            build.status.success(),
+            "cargo build -p perry-runtime failed\nstdout:\n{}\nstderr:\n{}",
+            String::from_utf8_lossy(&build.stdout),
+            String::from_utf8_lossy(&build.stderr)
+        );
+    });
+}
+
+fn runtime_dir() -> PathBuf {
+    ensure_runtime_archive();
+    target_debug_dir()
+}
+
+/// `f.test()` lives on line 4 of this fixture (1 = blank from the raw-string
+/// leading newline, 2 = `const`, 3 = `try {`, 4 = `f.test();`).
+const FIXTURE: &str = r#"
+const f: any = 5;
+try {
+  f.test();
+} catch (e: any) {
+  console.log("MSG:" + e.message);
+  console.log("STACK:" + e.stack);
+}
+"#;
+
+fn compile(root: &std::path::Path, extra_args: &[&str]) -> std::process::Output {
+    let entry = root.join("main.ts");
+    let output = root.join("main_bin");
+    let mut cmd = Command::new(perry_bin());
+    cmd.current_dir(root)
+        .arg("compile")
+        .arg(&entry)
+        .arg("-o")
+        .arg(&output)
+        .arg("--no-cache");
+    for a in extra_args {
+        cmd.arg(a);
+    }
+    cmd.env("PERRY_NO_AUTO_OPTIMIZE", "1");
+    cmd.env("PERRY_RUNTIME_DIR", runtime_dir());
+    cmd.output().expect("run perry compile")
+}
+
+#[test]
+fn debug_symbols_attaches_file_line_to_not_a_function_throw() {
+    let dir = tempfile::tempdir().expect("tempdir");
+    let root = dir.path();
+    std::fs::write(root.join("main.ts"), FIXTURE).expect("write entry");
+
+    let out = compile(root, &["--debug-symbols"]);
+    let stderr = String::from_utf8_lossy(&out.stderr);
+    assert!(
+        out.status.success(),
+        "compile --debug-symbols must succeed; stderr:\n{stderr}"
+    );
+
+    let bin = root.join("main_bin");
+    let run = Command::new(&bin).output().expect("run compiled binary");
+    let stdout = String::from_utf8_lossy(&run.stdout);
+
+    // The dynamic dispatch threw the expected TypeError.
+    assert!(
+        stdout.contains("MSG:") && stdout.contains("is not a function"),
+        "expected a 'is not a function' TypeError; got:\n{stdout}"
+    );
+    // The stack frame names the source file and the line of `f.test()` (4),
+    // not `<anonymous>`.
+    assert!(
+        stdout.contains("at main.ts:4"),
+        "expected 'at main.ts:4' frame with --debug-symbols; got:\n{stdout}"
+    );
+    assert!(
+        !stdout.contains("<anonymous>"),
+        "the location must replace the <anonymous> frame; got:\n{stdout}"
+    );
+}
+
+#[test]
+fn default_build_keeps_anonymous_frame() {
+    let dir = tempfile::tempdir().expect("tempdir");
+    let root = dir.path();
+    std::fs::write(root.join("main.ts"), FIXTURE).expect("write entry");
+
+    let out = compile(root, &[]);
+    let stderr = String::from_utf8_lossy(&out.stderr);
+    assert!(
+        out.status.success(),
+        "default compile must succeed; stderr:\n{stderr}"
+    );
+
+    let bin = root.join("main_bin");
+    let run = Command::new(&bin).output().expect("run compiled binary");
+    let stdout = String::from_utf8_lossy(&run.stdout);
+
+    assert!(
+        stdout.contains("is not a function"),
+        "expected a 'is not a function' TypeError; got:\n{stdout}"
+    );
+    // Default build is unchanged: the coarse <anonymous> frame, no file:line.
+    assert!(
+        stdout.contains("at <anonymous>"),
+        "default build must keep the <anonymous> frame; got:\n{stdout}"
+    );
+    assert!(
+        !stdout.contains("at main.ts:"),
+        "default build must NOT emit a source location; got:\n{stdout}"
+    );
+}