diff --git a/telethon/client/auth.py b/telethon/client/auth.py
index f10a3f65..170b626a 100644
--- a/telethon/client/auth.py
+++ b/telethon/client/auth.py
@@ -620,6 +620,7 @@ class AuthMethods:
 
         await self.disconnect()
         self.session.delete()
+        self.session = None
         return True
 
     async def edit_2fa(
diff --git a/telethon/client/telegrambaseclient.py b/telethon/client/telegrambaseclient.py
index 28e4485b..23708151 100644
--- a/telethon/client/telegrambaseclient.py
+++ b/telethon/client/telegrambaseclient.py
@@ -523,6 +523,9 @@ class TelegramBaseClient(abc.ABC):
                 except OSError:
                     print('Failed to connect')
         """
+        if self.session is None:
+            raise ValueError('TelegramClient instance cannot be reused after logging out')
+
         if not await self._sender.connect(self._connection(
             self.session.server_address,
             self.session.port,
@@ -603,6 +606,9 @@ class TelegramBaseClient(abc.ABC):
                 # You don't need to use this if you used "with client"
                 await client.disconnect()
         """
+        if self.session is None:
+            return  # already logged out and disconnected
+
         if self.loop.is_running():
             # Disconnect may be called from an event handler, which would
             # cancel itself during itself and never actually complete the