diff -r c27269c0d619 Objects/typeobject.c
--- a/Objects/typeobject.c	Wed Nov 09 09:43:37 2016 -0500
+++ b/Objects/typeobject.c	Wed Nov 09 12:48:42 2016 -0500
@@ -2501,14 +2501,15 @@
     Py_INCREF(name);
     et->ht_name = name;
     et->ht_slots = slots;
-    slots = NULL;
 
     /* Initialize tp_flags */
     type->tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HEAPTYPE |
         Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HAVE_FINALIZE;
-    if (base->tp_flags & Py_TPFLAGS_HAVE_GC)
+    if ((base->tp_flags & Py_TPFLAGS_HAVE_GC) || slots != NULL)
         type->tp_flags |= Py_TPFLAGS_HAVE_GC;
 
+    slots = NULL;
+
     /* Initialize essential fields */
     type->tp_as_async = &et->as_async;
     type->tp_as_number = &et->as_number;