diff --git a/aiogram/api/client/session/base.py b/aiogram/api/client/session/base.py
index f14d07bd..5ba7897f 100644
--- a/aiogram/api/client/session/base.py
+++ b/aiogram/api/client/session/base.py
@@ -19,7 +19,7 @@ class BaseSession(abc.ABC, Generic[_ProxyType]):
     def __init__(
         self,
         api: Optional[TelegramAPIServer] = None,
-        proxy: Optional[ProxyType] = None,
+        proxy: Optional[_ProxyType] = None,
         json_loads: Optional[Callable[[Any], Any]] = None,
         json_dumps: Optional[Callable[[Any], Any]] = None,
     ) -> None: