diff --git a/Objects/unionobject.c b/Objects/unionobject.c
index ad34dcad172..9804d87c66c 100644
--- a/Objects/unionobject.c
+++ b/Objects/unionobject.c
@@ -371,7 +371,7 @@ union_reduce(PyObject *self, PyObject *Py_UNUSED(ignored))
         return NULL;
     }
 
-    return Py_BuildValue("O(O)", from_args, alias->args);
+    return Py_BuildValue("N(O)", from_args, alias->args);
 }
 
 static PyMemberDef union_members[] = {