diff --git a/conntrackt/tests/test_models.py b/conntrackt/tests/test_models.py
--- a/conntrackt/tests/test_models.py
+++ b/conntrackt/tests/test_models.py
@@ -146,6 +146,19 @@ class InterfaceTest(TestCase):
 
         self.assertRaises(IntegrityError, duplicate.save)
 
+    def test_unique_address(self):
+        """
+        Test if unique address/netmask is enforced across same entity.
+        """
+
+        entity = Entity.objects.get(pk=1)
+
+        interface = entity.interface_set.get(pk=1)
+
+        duplicate = Interface(name="eth1", description="Duplicate address", entity=entity, address=interface.address, netmask=interface.netmask)
+
+        self.assertRaises(IntegrityError, duplicate.save)
+
     def test_representation_single(self):
         """
         Test representation of single IP address.