diff --git a/src/py/flwr/common/message.py b/src/py/flwr/common/message.py
index 8a92df4861db..1a49e80fe500 100644
--- a/src/py/flwr/common/message.py
+++ b/src/py/flwr/common/message.py
@@ -362,7 +362,7 @@ def __repr__(self) -> str:
         )
         return f"{self.__class__.__qualname__}({view})"
 
-    def _limit_task_res_ttl(self, message):
+    def _limit_task_res_ttl(self, message: Message) -> None:
         """Limit the TaskRes TTL to not exceed the expiration time of the TaskIns it
         replies to.