diff --git a/classes/advanced_search_form.php b/classes/advanced_search_form.php
index b142bfc..b4c8b07 100644
--- a/classes/advanced_search_form.php
+++ b/classes/advanced_search_form.php
@@ -126,7 +126,7 @@ public function __construct( $name, array $sections = array() )
         $this->addElement($sortField);
 
         // sort direction
-        $sortDirectionField = new RadioField('sort_direction'. self::PLUGIN_KEY);
+        $sortDirectionField = new RadioField('sort_direction', self::PLUGIN_KEY);
         $sortDirectionField->setLabel(OW::getLanguage()->text('forum', 'forms_search_sort_direction_field_label'));
         $sortDirectionField->addOptions(array(
            'increase' => OW::getLanguage()->text('forum', 'forms_search_sort_direction_field_value_increase'),