diff -r 6f41495e9336 Lib/pickle.py
--- a/Lib/pickle.py	Wed Dec 18 23:35:15 2013 -0700
+++ b/Lib/pickle.py	Thu Jul 03 17:03:41 2014 +0200
@@ -280,7 +280,9 @@
     module_name = getattr(obj, '__module__', None)
     if module_name is not None:
         return module_name
-    for module_name, module in sys.modules.items():
+    # Protect the iteration by using a list copy of sys.modules against dynamic
+    # modules that trigger imports of other modules upon calls to getattr.
+    for module_name, module in list(sys.modules.items()):
         if module_name == '__main__' or module is None:
             continue
         try: