diff --git a/lib/plugins/extension/helper/extension.php b/lib/plugins/extension/helper/extension.php
index 1f2c1af8383fb6f68abf01b4d7f1238acd24187c..339cc1bc65f1d6256195cba42f7d8c4228a60cd1 100644
--- a/lib/plugins/extension/helper/extension.php
+++ b/lib/plugins/extension/helper/extension.php
@@ -51,6 +51,7 @@ class helper_plugin_extension_extension extends DokuWiki_Plugin {
      * @return bool If some (local or remote) data was found
      */
     public function setExtension($id) {
+        $id = cleanID($id);
         $this->id   = $id;
         $this->base = $id;