diff --git a/src/uu/numfmt/src/format.rs b/src/uu/numfmt/src/format.rs
index 77febdaaa41..2c21d93f2fb 100644
--- a/src/uu/numfmt/src/format.rs
+++ b/src/uu/numfmt/src/format.rs
@@ -159,6 +159,17 @@ fn parse_number_part(s: &str, input: &str) -> Result<ParsedNumber> {
         return Err(translate!("numfmt-error-invalid-number", "input" => input.quote()));
     }
 
+    // GNU numfmt does not accept a leading '+' sign nor scientific notation, but
+    // Rust's i128/f64 parsers do, so "+5" and "1e-3" would slip through. Reject
+    // them here, mirroring GNU's two distinct diagnostics (a leading sign is an
+    // "invalid number", an exponent is an "invalid suffix in input").
+    if s.starts_with('+') {
+        return Err(translate!("numfmt-error-invalid-number", "input" => input.quote()));
+    }
+    if s.bytes().any(|b| b == b'e' || b == b'E') {
+        return Err(translate!("numfmt-error-invalid-suffix", "input" => input.quote()));
+    }
+
     if let Ok(n) = s.parse::<i128>() {
         return Ok(ParsedNumber::ExactInt(n));
     }
diff --git a/tests/by-util/test_numfmt.rs b/tests/by-util/test_numfmt.rs
index 33d810af269..2227dad61dc 100644
--- a/tests/by-util/test_numfmt.rs
+++ b/tests/by-util/test_numfmt.rs
@@ -185,6 +185,26 @@ fn test_header_error_if_negative() {
         .stderr_is("numfmt: invalid header value '-3'\n");
 }
 
+#[test]
+fn test_reject_leading_plus_and_scientific_notation() {
+    // GNU numfmt rejects a leading '+' as an invalid number and rejects scientific
+    // notation as an invalid suffix; Rust's parsers accept both, so guard against it.
+    for input in ["+5", "+5K", "+1e-3"] {
+        new_ucmd!()
+            .arg("--from=auto")
+            .pipe_in(format!("{input}\n"))
+            .fails_with_code(2)
+            .stderr_is(format!("numfmt: invalid number: '{input}'\n"));
+    }
+    for input in ["1e-3", "1e+3", "5e-5", "1.0e-2", "-1e-5"] {
+        new_ucmd!()
+            .arg("--from=auto")
+            .pipe_in(format!("{input}\n"))
+            .fails_with_code(2)
+            .stderr_is(format!("numfmt: invalid suffix in input: '{input}'\n"));
+    }
+}
+
 #[test]
 fn test_negative() {
     new_ucmd!()