diff --git a/src/tools/compiletest/src/header.rs b/src/tools/compiletest/src/header.rs
index 52102e939f7ec..abfb89641bf92 100644
--- a/src/tools/compiletest/src/header.rs
+++ b/src/tools/compiletest/src/header.rs
@@ -973,7 +973,8 @@ fn iter_header(
                         directive: original_directive_line,
                     });
                     continue;
-                } else {
+                // Too prone to false positives to handle Makefile `#` directives...1
+                } else if testfile.extension().is_some_and(|e| e == "rs") {
                     *poisoned = true;
                     eprintln!(
                         "error: detected unknown compiletest test directive `{}` in {}:{}",
@@ -997,7 +998,7 @@ fn iter_header(
                     directive: original_directive_line,
                 });
                 continue;
-            } else {
+            } else if testfile.extension().is_some_and(|e| e == "rs") {
                 *poisoned = true;
                 eprintln!(
                     "error: detected unknown compiletest test directive `{}` in {}:{}",