diff --git a/aiogram/utils/chat_action.py b/aiogram/utils/chat_action.py
index 517d0352..aa80933f 100644
--- a/aiogram/utils/chat_action.py
+++ b/aiogram/utils/chat_action.py
@@ -98,7 +98,7 @@ class ChatActionSender:
             )
             self._closed_event.set()
 
-    async def _initial_action(self):
+    async def _initial_action(self) -> None:
         """Process initial action.
 
         If there's no initial sleep, start worker immediately.