diff --git a/Lib/collections.py b/Lib/collections.py
index 4028983..a1e8ed9 100644
--- a/Lib/collections.py
+++ b/Lib/collections.py
@@ -58,9 +58,13 @@
 
     def __reduce__(self):
         items = [[k, self[k]] for k in self]
+        tmp = self.__keys
+        del self.__keys
         inst_dict = vars(self).copy()
-        inst_dict.pop('__keys', None)
-        return (self.__class__, (items,), inst_dict)
+        self.__keys = tmp
+        if inst_dict:
+            return (self.__class__, (items,), inst_dict)
+        return self.__class__, (items,)
 
     setdefault = MutableMapping.setdefault
     update = MutableMapping.update