diff -r dbdc95931fa7 Objects/typeobject.c
--- a/Objects/typeobject.c	Sat Jun 25 16:43:26 2016 -0700
+++ b/Objects/typeobject.c	Sun Jun 26 09:25:55 2016 +0300
@@ -4908,7 +4908,9 @@ PyType_Ready(PyTypeObject *type)
     }
 
     /* All bases of statically allocated type should be statically allocated */
-    if (!(type->tp_flags & Py_TPFLAGS_HEAPTYPE))
+    if (!(type->tp_flags & Py_TPFLAGS_HEAPTYPE)) {
+        bases = type->tp_bases;
+        n = PyTuple_GET_SIZE(bases);
         for (i = 0; i < n; i++) {
             PyObject *b = PyTuple_GET_ITEM(bases, i);
             if (PyType_Check(b) &&
@@ -4920,6 +4922,7 @@ PyType_Ready(PyTypeObject *type)
                 goto error;
             }
         }
+    }
 
     /* Sanity check for tp_free. */
     if (PyType_IS_GC(type) && (type->tp_flags & Py_TPFLAGS_BASETYPE) &&