diff --git a/admin/languages_installed.php b/admin/languages_installed.php
index d173ff6f7..d8573bfe8 100644
--- a/admin/languages_installed.php
+++ b/admin/languages_installed.php
@@ -21,6 +21,9 @@ $languages = new languages();
 $languages->get_db_languages();
 
 //--------------------------------------------------perform requested actions
+check_input_parameter('action', $_GET, false, '/^(activate|deactivate|set_default|delete)$/');
+check_input_parameter('language', $_GET, false, '/^('.join('|', array_keys($languages->fs_languages)).')$/');
+
 if (isset($_GET['action']) and isset($_GET['language']))
 {
   $page['errors'] = $languages->perform_action($_GET['action'], $_GET['language']);