diff --git a/tempest/api/compute/servers/test_virtual_interfaces.py b/tempest/api/compute/servers/test_virtual_interfaces.py
index 85f0041..7aa6d34 100644
--- a/tempest/api/compute/servers/test_virtual_interfaces.py
+++ b/tempest/api/compute/servers/test_virtual_interfaces.py
@@ -57,4 +57,5 @@
         for virt_iface in virt_ifaces['virtual_interfaces']:
             mac_address = virt_iface['mac_address']
             self.assertTrue(netaddr.valid_mac(mac_address),
-                            "Invalid mac address detected.")
+                            "Invalid mac address detected. mac address: %s"
+                            % mac_address)