diff -r 90d318d40a83 -r d08d2744353a Objects/object.c
--- a/Objects/object.c	Mon Dec 05 18:23:27 2016 +0100
+++ b/Objects/object.c	Mon Dec 05 22:44:10 2016 +0100
@@ -930,6 +930,8 @@
     PyUnicode_InternInPlace(&name);
     if (tp->tp_setattro != NULL) {
         err = (*tp->tp_setattro)(v, name, value);
+        if (PyType_Check(v))
+            PyType_Modified((PyTypeObject*)v);
         Py_DECREF(name);
         return err;
     }