Index: Objects/typeobject.c
===================================================================
--- Objects/typeobject.c	(revision 66056)
+++ Objects/typeobject.c	(working copy)
@@ -4633,6 +4633,11 @@
 
 	if (res == NULL)
 		return -1;
+	if (!PyLong_Check(res)) {
+		PyErr_SetString(PyExc_TypeError, 
+				"__len__() should return an int");
+		return -1;
+	}
 	len = PyLong_AsSsize_t(res);
 	Py_DECREF(res);
 	if (len < 0) {