diff -r 3744b6ad8c3f Lib/pickle.py
--- a/Lib/pickle.py	Wed Jul 02 08:36:19 2014 -0400
+++ b/Lib/pickle.py	Wed Jul 02 14:59:12 2014 +0200
@@ -280,7 +280,7 @@
     module_name = getattr(obj, '__module__', None)
     if module_name is not None:
         return module_name
-    for module_name, module in sys.modules.items():
+    for module_name, module in list(sys.modules.items()):
         if module_name == '__main__' or module is None:
             continue
         try: