diff --git a/mautrix_telegram/commands/auth.py b/mautrix_telegram/commands/auth.py
index 3f57cbb9..1f37f13c 100644
--- a/mautrix_telegram/commands/auth.py
+++ b/mautrix_telegram/commands/auth.py
@@ -299,7 +299,7 @@ async def sign_in(evt: CommandEvent, **sign_in_info) -> Dict:
         await evt.sender.ensure_started(even_if_no_session=True)
         user = await evt.sender.client.sign_in(**sign_in_info)
         existing_user = u.User.get_by_tgid(user.id)
-        if existing_user != evt.sender:
+        if existing_user and existing_user != evt.sender:
             await existing_user.log_out()
             await evt.reply(f"[{existing_user.displayname}]"
                             f"(https://matrix.to/#/{existing_user.mxid})"
diff --git a/mautrix_telegram/web/common/auth_api.py b/mautrix_telegram/web/common/auth_api.py
index 700b26c1..a91ea682 100644
--- a/mautrix_telegram/web/common/auth_api.py
+++ b/mautrix_telegram/web/common/auth_api.py
@@ -110,7 +110,7 @@ class AuthAPI(abc.ABC):
 
     async def postprocess_login(self, user: User, user_info) -> None:
         existing_user = User.get_by_tgid(user_info.id)
-        if existing_user != user:
+        if existing_user and existing_user != user:
             await existing_user.log_out()
         asyncio.ensure_future(user.post_login(user_info), loop=self.loop)
         if user.command_status and user.command_status["action"] == "Login":