diff --git a/src/memory/persistent.py b/src/memory/persistent.py
index 1482eaaa..4b5668b8 100644
--- a/src/memory/persistent.py
+++ b/src/memory/persistent.py
@@ -85,6 +85,9 @@ class PersistentDict(object):
     def __contains__(self, key):
         return self._cache.__contains__(key)
 
+    def __iter__(self):
+        return self._cache.__iter__()
+
     def __getitem__(self, key):
         return self._cache.__getitem__(key)