diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index f40807a..a50e456 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -22,11 +22,17 @@ jobs:
         os: [ubuntu-latest, windows-latest, macOS-latest, windows-11-arm]
         mode: ["--release", "-Zminimal-versions", ""]
         manifest: ["psm/Cargo.toml", "Cargo.toml"]
+        # Pedantic flags
+        cflags: ["-Werror -Wundef", ""]
         exclude:
           - rust_toolchain: stable
             mode: -Zminimal-versions
           - rust_toolchain: 1.91.0
             mode: -Zminimal-versions
+          - os: windows-latest
+            cflags: "-Werror -Wundef"
+          - os: windows-11-arm
+            cflags: "-Werror -Wundef"
         include:
           - os: windows-latest
             extra_target: i686-pc-windows-msvc
@@ -34,6 +40,8 @@ jobs:
             rust_toolchain: nightly
             extra_target: arm64ec-pc-windows-msvc
     timeout-minutes: 10
+    env:
+      CFLAGS: ${{ matrix.cflags }}
     steps:
       - uses: actions/checkout@v4
       - name: Install Rust ${{ matrix.rust_toolchain }}
@@ -101,6 +109,7 @@ jobs:
           args: --target=${{ matrix.rust_target }} --manifest-path=${{ matrix.manifest }} -- --nocapture
         env:
           CC: ${{ matrix.clang_cl }}
+          CFLAGS: "-Werror -Wundef"
 
   windows-gnu-test:
     name: Test ${{ matrix.manifest }} on ${{ matrix.rust_target }} with ${{ matrix.rust_toolchain }}
@@ -139,6 +148,8 @@ jobs:
         with:
           command: test
           args: --target ${{ matrix.rust_target }} --manifest-path=${{ matrix.manifest }}
+        env:
+          CFLAGS: "-Werror -Wundef"
 
   cross-windows-gnullvm-check:
     name: Check ${{ matrix.manifest }} to ${{ matrix.rust_target }} with stable
diff --git a/psm/src/arch/aarch_aapcs64.s b/psm/src/arch/aarch_aapcs64.s
index ee10f8a..b6a2e93 100644
--- a/psm/src/arch/aarch_aapcs64.s
+++ b/psm/src/arch/aarch_aapcs64.s
@@ -3,14 +3,14 @@
 
 .text
 
-#if CFG_TARGET_OS_darwin || CFG_TARGET_OS_macos || CFG_TARGET_OS_ios
+#if defined(CFG_TARGET_OS_darwin) || defined(CFG_TARGET_OS_macos) || defined(CFG_TARGET_OS_ios)
 
 #define GLOBL(fnname) .globl _##fnname
 #define TYPE(fnname)
 #define FUNCTION(fnname) _##fnname
 #define END_FUNCTION(fnname)
 
-#elif CFG_TARGET_OS_windows
+#elif defined(CFG_TARGET_OS_windows)
 
 #define GLOBL(fnname) .globl fnname
 #define TYPE(fnname)
diff --git a/psm/src/arch/arm_aapcs.s b/psm/src/arch/arm_aapcs.s
index 8ab5cae..3a01ae0 100644
--- a/psm/src/arch/arm_aapcs.s
+++ b/psm/src/arch/arm_aapcs.s
@@ -4,7 +4,7 @@
 .text
 .syntax unified
 
-#if CFG_TARGET_OS_darwin || CFG_TARGET_OS_macos || CFG_TARGET_OS_ios
+#if defined(CFG_TARGET_OS_darwin) || defined(CFG_TARGET_OS_macos) || defined(CFG_TARGET_OS_ios)
 
 #define GLOBL(fnname) .globl _##fnname
 #define THUMBTYPE(fnname) .thumb_func _##fnname
diff --git a/psm/src/arch/x86.s b/psm/src/arch/x86.s
index 5eec45c..d4b7b39 100644
--- a/psm/src/arch/x86.s
+++ b/psm/src/arch/x86.s
@@ -4,7 +4,7 @@
 
 .text
 
-#if CFG_TARGET_OS_darwin || CFG_TARGET_OS_macos || CFG_TARGET_OS_ios
+#if defined(CFG_TARGET_OS_darwin) || defined(CFG_TARGET_OS_macos) || defined(CFG_TARGET_OS_ios)
 
 #define GLOBL(fnname) .globl _##fnname
 #define TYPE(fnname)
diff --git a/psm/src/arch/x86_64.s b/psm/src/arch/x86_64.s
index 9a9b531..3c876d0 100644
--- a/psm/src/arch/x86_64.s
+++ b/psm/src/arch/x86_64.s
@@ -4,7 +4,7 @@
 
 .text
 
-#if CFG_TARGET_OS_darwin || CFG_TARGET_OS_macos || CFG_TARGET_OS_ios
+#if defined(CFG_TARGET_OS_darwin) || defined(CFG_TARGET_OS_macos) || defined(CFG_TARGET_OS_ios)
 
 #define GLOBL(fnname) .globl _##fnname
 #define TYPE(fnname)