diff --git a/src/etc/inc/plugins.inc.d/openvpn.inc b/src/etc/inc/plugins.inc.d/openvpn.inc
index 14d165c63..dc7834625 100644
--- a/src/etc/inc/plugins.inc.d/openvpn.inc
+++ b/src/etc/inc/plugins.inc.d/openvpn.inc
@@ -1071,7 +1071,7 @@ function openvpn_csc_conf_write($settings, $server, $target_filename = null)
         if ($server['dev_mode'] == 'tun' && empty($server['topology_subnet'])) {
             $conf .= "ifconfig-ipv6-push {$ipv6_2} {$ipv6_1}\n";
         } else {
-            $conf .= "ifconfig-ipv6-push {$ipv6_2} {$prefix}\n";
+            $conf .= "ifconfig-ipv6-push {$ipv6_2}/{$prefix}\n";
         }
     }