diff --git a/src/opnsense/mvc/app/library/OPNsense/Firewall/Util.php b/src/opnsense/mvc/app/library/OPNsense/Firewall/Util.php
index 5633ad42a..58bca1317 100644
--- a/src/opnsense/mvc/app/library/OPNsense/Firewall/Util.php
+++ b/src/opnsense/mvc/app/library/OPNsense/Firewall/Util.php
@@ -339,6 +339,16 @@ class Util
         return md5(json_encode($rule));
     }
 
+    /**
+     * convert ipv4 cidr to netmask e.g. 24 --> 255.255.255.0
+     * @param int $bits ipv4 bits
+     * @return string netmask
+     */
+    public static function CIDRToMask($bits)
+    {
+        return long2ip(0xFFFFFFFF << (32 - $bits));
+    }
+
     /**
      * Find the smallest possible subnet mask for given IP range
      * @param array ips (start, end)