diff --git a/models.py b/models.py
index e0f9a6e..0b7cc5d 100644
--- a/models.py
+++ b/models.py
@@ -39,7 +39,7 @@ class User(UserMixin, db.Model):
 
     # Multi-Container Support (explicit primaryjoin wegen mehrerer FKs zu User)
     containers = db.relationship('UserContainer',
-                                foreign_keys='UserContainer.user_id',
+                                foreign_keys=['UserContainer.user_id'],
                                 primaryjoin='User.id==UserContainer.user_id',
                                 back_populates='user',
                                 cascade='all, delete-orphan')