diff --git a/src/judas_server/backend/handler/ack_handler.py b/src/judas_server/backend/handler/ack_handler.py
index 8204be0..1756b80 100644
--- a/src/judas_server/backend/handler/ack_handler.py
+++ b/src/judas_server/backend/handler/ack_handler.py
@@ -1,4 +1,5 @@
 # -*- coding: utf-8 -*-
+from __future__ import annotations
 
 from typing import TYPE_CHECKING