diff --git a/mac.go b/mac.go
index cd9038b..e1a3bf3 100644
--- a/mac.go
+++ b/mac.go
@@ -43,7 +43,7 @@ func (i *iface) ProcMAC() (err error) {
 	_, err = sb.WriteString(i.pfx)
 	_, err = sb.WriteString("x")
 	for _, v := range addr {
-		_, err = sb.WriteString(fmt.Sprintf("%x", v))
+		_, err = sb.WriteString(fmt.Sprintf("%02x", v))
 	}
 
 	i.names[IfNameMAC] = sb.String()