diff --git a/matrix_appservice_kakaotalk/user.py b/matrix_appservice_kakaotalk/user.py
index 8e11c35..dbe9b8a 100644
--- a/matrix_appservice_kakaotalk/user.py
+++ b/matrix_appservice_kakaotalk/user.py
@@ -317,6 +317,8 @@ class User(DBUser, BaseUser):
                         oauth_credential = await Client.login(uuid=uuid, form=form, forced=True)
                     except OAuthException as e:
                         latest_exc = e
+                else:
+                    return False
             if oauth_credential:
                 self.oauth_credential = oauth_credential
                 await self.save()