diff --git a/src/AjaxHandler/GroupingCheckboxFactory.php b/src/AjaxHandler/GroupingCheckboxFactory.php
index c7b9533da6a6cd7f1cf00b7d7f1d830dbefdd267..54d62c38c3a9b459ff6c00aee473fc06377093e6 100644
--- a/src/AjaxHandler/GroupingCheckboxFactory.php
+++ b/src/AjaxHandler/GroupingCheckboxFactory.php
@@ -35,7 +35,7 @@ class GroupingCheckboxFactory
      * @param ContainerInterface $container
      * @return \VuFindResultsGrouping\AjaxHandler\GroupingCheckbox
      */
-    public static function __invoke(ContainerInterface $container)
+    public function __invoke(ContainerInterface $container)
     {
         return new GroupingCheckbox(
             $container->get('VuFindResultsGrouping\Config\Grouping')