diff --git a/aiogram/bot/api.py b/aiogram/bot/api.py
index e5982f07..047e761a 100644
--- a/aiogram/bot/api.py
+++ b/aiogram/bot/api.py
@@ -143,7 +143,7 @@ async def request(session, token, method, data=None, files=None, continue_retry=
         async with session.post(url, data=data, **kwargs) as response:
             return await _check_result(method, response)
     except aiohttp.ClientError as e:
-        raise TelegramAPIError(f"aiohttp client throws an error: {e.__class__.__name__}: {e}")
+        raise NetworkError(f"aiohttp client throws an error: {e.__class__.__name__}: {e}")
     except RetryAfter as e:
         if continue_retry:
             await asyncio.sleep(e.timeout)
diff --git a/aiogram/exceptions.py b/aiogram/exceptions.py
index 4fbb4cf9..fdc18bb6 100644
--- a/aiogram/exceptions.py
+++ b/aiogram/exceptions.py
@@ -2,7 +2,8 @@ def _clean_message(text):
     return text. \
         lstrip('Error: '). \
         lstrip('[Error]: '). \
-        lstrip('Bad Request: ')
+        lstrip('Bad Request: '). \
+        capitalize()
 
 
 class TelegramAPIError(Exception):
@@ -28,11 +29,11 @@ class NetworkError(TelegramAPIError):
 
 class RetryAfter(TelegramAPIError):
     def __init__(self, retry_after):
-        super(RetryAfter, self).__init__(f"Flood control exceeded. Retry in {retry_after} seconds")
+        super(RetryAfter, self).__init__(f"Flood control exceeded. Retry in {retry_after} seconds.")
         self.timeout = retry_after
 
 
 class MigrateToChat(TelegramAPIError):
     def __init__(self, chat_id):
-        super(MigrateToChat, self).__init__(f"The group has been migrated to a supergroup. New id: {chat_id}")
+        super(MigrateToChat, self).__init__(f"The group has been migrated to a supergroup. New id: {chat_id}.")
         self.migrate_to_chat_id = chat_id