diff --git a/conf/plugins.required.php b/conf/plugins.required.php
index a2950b760..75336da2e 100644
--- a/conf/plugins.required.php
+++ b/conf/plugins.required.php
@@ -5,6 +5,7 @@
  * It is not recommended to change this file, as it is overwritten on DokuWiki upgrades.
  */
 $plugins['acl']               = 1;
+$plugins['authplain']         = 1;
 $plugins['extension']         = 1;
 $plugins['config']            = 1;
 $plugins['usermanager']       = 1;
diff --git a/lib/plugins/extension/helper/extension.php b/lib/plugins/extension/helper/extension.php
index be29f95d8..2a7119189 100644
--- a/lib/plugins/extension/helper/extension.php
+++ b/lib/plugins/extension/helper/extension.php
@@ -102,11 +102,15 @@ class helper_plugin_extension_extension extends DokuWiki_Plugin {
     }
 
     /**
-     * If the extension is protected
+     * If the extension is protected against any modification (disable/uninstall)
      *
      * @return bool if the extension is protected
      */
     public function isProtected() {
+        // never allow deinstalling the current auth plugin:
+        global $conf;
+        if ($this->id == $conf['authtype']) return true;
+
         /** @var Doku_Plugin_Controller $plugin_controller */
         global $plugin_controller;
         $cascade = $plugin_controller->getCascade();