Index: Objects/typeobject.c
===================================================================
--- Objects/typeobject.c	(revision 45317)
+++ Objects/typeobject.c	(working copy)
@@ -583,8 +583,16 @@
 		assert(base);
 	}
 
-	/* There's no need to clear the instance dict (if any);
-	   the collector will call its tp_clear handler. */
+	/* Clear the instance dict (if any), to break cycles involving only
+	   __dict__ slots (as in the case 'self.__dict__ == self'). */
+	if (type->tp_dictoffset != base->tp_dictoffset) {
+		PyObject **dictptr = _PyObject_GetDictPtr(self);
+		if (dictptr && *dictptr) {
+			PyObject *dict = *dictptr;
+			*dictptr = NULL;
+			Py_DECREF(dict);
+		}
+	}
 
 	if (baseclear)
 		return baseclear(self);