diff --git a/Classes/Hooks/ButtonBarHook.php b/Classes/Hooks/ButtonBarHook.php
index 9e711617..29eb7fdd 100644
--- a/Classes/Hooks/ButtonBarHook.php
+++ b/Classes/Hooks/ButtonBarHook.php
@@ -37,7 +37,7 @@ public function getButtons(array $params, ButtonBar $buttonBar)
             );
 
             if (
-                $page['module'] === 'glossary'
+                isset($page['module']) && $page['module'] === 'glossary'
                 && $this->getBackendUserAuthentication()
                     ->check('tables_modify', 'tx_wvdeepltranslate_glossaryentry')
             ) {