diff --git a/backend/app/models/domain.py b/backend/app/models/domain.py
index 4373e64..5f04ce3 100644
--- a/backend/app/models/domain.py
+++ b/backend/app/models/domain.py
@@ -70,7 +70,7 @@ class Domain(db.Model):
 
     id = db.Column(db.Integer, primary_key=True)
     domain_name = db.Column(db.String(255), unique=True, nullable=False, index=True)
-    customer_id = db.Column(db.Integer, nullable=False, index=True)
+    customer_id = db.Column(db.Integer, db.ForeignKey('customers.id'), nullable=False, index=True)
 
     # Cloudflare Configuration
     use_cloudflare = db.Column(db.Boolean, default=True)