diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index b042e64a188..447e561c0d4 100644
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -8395,7 +8395,7 @@ type_ready(PyTypeObject *type, int initial)
     }
 
     /* All done -- set the ready flag */
-    type->tp_flags = type->tp_flags | Py_TPFLAGS_READY;
+    type->tp_flags |= Py_TPFLAGS_READY;
     stop_readying(type);
 
     assert(_PyType_CheckConsistency(type));