diff --git a/includes/polling/ports.inc.php b/includes/polling/ports.inc.php
index ae318153b..3be67e15c 100644
--- a/includes/polling/ports.inc.php
+++ b/includes/polling/ports.inc.php
@@ -352,7 +352,7 @@ foreach ($ports as $port) {
             }
         }//end foreach
 
-        if (($port['update']['ifAlias'] == '' || $port['update']['ifAlias'] == NULL) && $config['os'][$os]['ifalias_null'] == 1) {
+        if (($port['update']['ifAlias'] == '' || $port['update']['ifAlias'] == NULL) && $config['os'][$device['os']]['ifalias_null'] == 1) {
             $port['update']['ifAlias'] = $port['ifDescr'];
             d_echo('Using ifDescr due to ifAlias being NULL');
         }