diff --git a/netjsonconfig/schema.py b/netjsonconfig/schema.py
index 31539e52c..0c7a7d6b6 100644
--- a/netjsonconfig/schema.py
+++ b/netjsonconfig/schema.py
@@ -146,6 +146,8 @@
                 "mac": {
                     "type": "string",
                     "title": "mac address",
+                    "minLength": 17,
+                    "maxLength": 17,
                     "propertyOrder": 2,
                 },
                 "mtu": {