diff --git a/aiogram/utils/handlers_in_use.py b/aiogram/utils/handlers_in_use.py
index b50e89fa..53e8e63d 100644
--- a/aiogram/utils/handlers_in_use.py
+++ b/aiogram/utils/handlers_in_use.py
@@ -1,19 +1,21 @@
 
+from aiogram.dispatcher.router import Router
 from itertools import chain
-from typing import List
+from typing import List, cast
 from aiogram.dispatcher.dispatcher import Dispatcher
 
 AIOGRAM_INTERNAL_HANDLERS = ['update', 'error', ]
 
 
 def get_handlers_in_use(dispatcher: Dispatcher, handlers_to_skip: List[str] = AIOGRAM_INTERNAL_HANDLERS) -> List[str]:
-    handlers_in_use = []
+    handlers_in_use: List[str] = []
 
     for router in [dispatcher.sub_routers, dispatcher]:
         if (isinstance(router, list)):
             if (router):
                 handlers_in_use.extend(chain(*list(map(get_handlers_in_use, router))))
         else:
+            router = cast(Router, router)
             for update_name, observer in router.observers.items():
                 if (observer.handlers and update_name not in [*handlers_to_skip, *handlers_in_use]):
                     handlers_in_use.append(update_name)