diff --git a/python/wpt/update.py b/python/wpt/update.py
index 42c424eb9e2..96efa483a7f 100644
--- a/python/wpt/update.py
+++ b/python/wpt/update.py
@@ -60,9 +60,7 @@ def remove_unused_metadata():
     for meta_root in META_ROOTS:
         for base_dir, dir_names, files in os.walk(meta_root):
             # Skip recursing into any directories that were previously found to be missing.
-            if base_dir in unused_dirs:
-                # Skip processing any subdirectories of known missing directories.
-                unused_dirs += [os.path.join(base_dir, x) for x in dir_names]
+            if any([os.path.commonpath([base_dir, unused_dir]) == unused_dir for unused_dir in unused_dirs]):
                 continue
 
             for dir_name in dir_names: