diff --git a/testing/web-platform/tests/tools/manifest/sourcefile.py b/testing/web-platform/tests/tools/manifest/sourcefile.py
index 11779532c1e55..b324bf22dd382 100644
--- a/testing/web-platform/tests/tools/manifest/sourcefile.py
+++ b/testing/web-platform/tests/tools/manifest/sourcefile.py
@@ -989,9 +989,9 @@ def manifest_items(self):
 
         if drop_cached and "__cached_properties__" in self.__dict__:
             cached_properties = self.__dict__["__cached_properties__"]
-            for key in cached_properties:
-                if str(key) in self.__dict__:
-                    del self.__dict__[str(key)]
+            for prop in cached_properties:
+                if prop in self.__dict__:
+                    del self.__dict__[prop]
             del self.__dict__["__cached_properties__"]
 
         return rv