diff --git a/src/etc/inc/filter.inc b/src/etc/inc/filter.inc
index 964bd24c8..6d98cf8d7 100644
--- a/src/etc/inc/filter.inc
+++ b/src/etc/inc/filter.inc
@@ -910,7 +910,7 @@ function filter_generate_optcfg_array()
         if (isset($oc['alias-subnet'])) {
             $oic['alias-subnet'] = $oc['alias-subnet'];
         } else {
-            $oc['alias-subnet'] = null;
+            $oic['alias-subnet'] = null;
         }
         if (isset($oc['gateway'])) {
             $oic['gateway'] = $oc['gateway'];