diff --git a/aiogram/api/client/session/base.py b/aiogram/api/client/session/base.py
index 450b958d..b99e9e4b 100644
--- a/aiogram/api/client/session/base.py
+++ b/aiogram/api/client/session/base.py
@@ -12,42 +12,37 @@ from ...methods import Response, TelegramMethod
 from ..telegram import PRODUCTION, TelegramAPIServer
 
 T = TypeVar("T")
-PT = TypeVar("PT")
+_JSON_LOADS = Callable[..., Any]
+_JSON_DUMPS = Callable[..., str]
 
 
 class BaseSession(abc.ABC):
     _api: TelegramAPIServer
-    _json_loads: Callable[..., Any]
-    _json_dumps: Callable[..., str]
+    _json_loads: _JSON_LOADS
+    _json_dumps: _JSON_DUMPS
 
     @property
-    def api(self) -> TelegramAPIServer:  # pragma: no cover
-        if not hasattr(self, "_api"):
-            return PRODUCTION
-        return self._api
+    def api(self) -> TelegramAPIServer:
+        return getattr(self, "_api", PRODUCTION)  # type: ignore
 
     @api.setter
-    def api(self, value: TelegramAPIServer) -> None:  # pragma: no cover
+    def api(self, value: TelegramAPIServer) -> None:
         self._api = value
 
     @property
-    def json_loads(self) -> Callable[..., Any]:  # pragma: no cover
-        if not hasattr(self, "_json_loads"):
-            return json.loads
-        return self._json_loads
+    def json_loads(self) -> _JSON_LOADS:
+        return getattr(self, "_json_loads", json.loads)  # type: ignore
 
     @json_loads.setter
-    def json_loads(self, value: Callable[..., Any]) -> None:  # pragma: no cover
+    def json_loads(self, value: _JSON_LOADS) -> None:
         self._json_loads = value  # type: ignore
 
     @property
-    def json_dumps(self) -> Callable[..., str]:  # pragma: no cover
-        if not hasattr(self, "_json_dumps"):
-            return json.dumps
-        return self._json_dumps
+    def json_dumps(self) -> _JSON_DUMPS:
+        return getattr(self, "_json_dumps", json.dumps)  # type: ignore
 
     @json_dumps.setter
-    def json_dumps(self, value: Callable[..., str]) -> None:  # pragma: no cover
+    def json_dumps(self, value: _JSON_DUMPS) -> None:
         self._json_dumps = value  # type: ignore
 
     @classmethod
diff --git a/tests/test_api/test_client/test_session/test_base_session.py b/tests/test_api/test_client/test_session/test_base_session.py
index 9d775123..43f1d7d5 100644
--- a/tests/test_api/test_client/test_session/test_base_session.py
+++ b/tests/test_api/test_client/test_session/test_base_session.py
@@ -1,4 +1,5 @@
 import datetime
+import json
 from typing import AsyncContextManager, AsyncGenerator
 
 import pytest
@@ -35,6 +36,26 @@ class TestBaseSession:
         session = CustomSession()
         assert session.api == PRODUCTION
 
+    def test_default_props(self):
+        session = CustomSession()
+        assert session.api == PRODUCTION
+        assert session.json_loads == json.loads
+        assert session.json_dumps == json.dumps
+
+        def custom_loads(*_):
+            return json.loads
+
+        def custom_dumps(*_):
+            return json.dumps
+
+        session.json_dumps = custom_dumps
+        assert session.json_dumps == custom_dumps == session._json_dumps
+        session.json_loads = custom_loads
+        assert session.json_loads == custom_loads == session._json_loads
+
+        different_session = CustomSession()
+        assert all(not hasattr(different_session, attr) for attr in ("_json_loads", "_json_dumps", "_api"))
+
     def test_init_custom_api(self):
         api = TelegramAPIServer(
             base="http://example.com/{token}/{method}",