diff --git a/models.py b/models.py
index 95eafcb..e0f9a6e 100644
--- a/models.py
+++ b/models.py
@@ -152,9 +152,14 @@ class UserContainer(db.Model):
     blocked_at = db.Column(db.DateTime, nullable=True)
     blocked_by = db.Column(db.Integer, db.ForeignKey('user.id', ondelete='SET NULL'), nullable=True)
 
-    # Relationships
-    user = db.relationship('User', foreign_keys=['user_id'], back_populates='containers')
-    blocker = db.relationship('User', foreign_keys=['blocked_by'])
+    # Relationships (explicit primaryjoin wegen mehrerer FKs zu User)
+    user = db.relationship('User',
+                          foreign_keys=['user_id'],
+                          primaryjoin='UserContainer.user_id==User.id',
+                          back_populates='containers')
+    blocker = db.relationship('User',
+                             foreign_keys=['blocked_by'],
+                             primaryjoin='UserContainer.blocked_by==User.id')
 
     # Unique: Ein User kann nur einen Container pro Typ haben
     __table_args__ = (