diff -r 1b58f14f5d60 Modules/_collectionsmodule.c
--- a/Modules/_collectionsmodule.c	Wed Nov 20 17:44:28 2013 +0200
+++ b/Modules/_collectionsmodule.c	Thu Nov 21 00:24:58 2013 +0800
@@ -1682,7 +1682,7 @@
             newdefault = PyTuple_GET_ITEM(args, 0);
             if (!PyCallable_Check(newdefault) && newdefault != Py_None) {
                 PyErr_SetString(PyExc_TypeError,
-                    "first argument must be callable");
+                    "first argument must be callable or None");
                 return -1;
             }
         }