diff --git a/importlib_metadata/__init__.py b/importlib_metadata/__init__.py
index d1b0d92d..58bbd95e 100644
--- a/importlib_metadata/__init__.py
+++ b/importlib_metadata/__init__.py
@@ -672,6 +672,7 @@ def origin(self):
         return self._load_json('direct_url.json')
 
     def _load_json(self, filename):
+        # Deferred for performance (python/importlib_metadata#503)
         import json
 
         return pass_none(json.loads)(