diff --git a/conntrackt/models.py b/conntrackt/models.py
--- a/conntrackt/models.py
+++ b/conntrackt/models.py
@@ -197,8 +197,10 @@ class Interface(models.Model):
     netmask = models.IPAddressField(default='255.255.255.255')
 
     class Meta:
-        # Enforce uniqueness of interface name in an entity.
-        unique_together = ("name", "entity")
+        # Enforce uniqueness of interface name in an entity. Enforce uniqueness
+        # of IP address in a subnet for an entity.
+        unique_together = (("name", "entity"),
+                           ("entity", "address", "netmask"),)
 
     def __unicode__(self):
         """