diff --git a/enrol/guest/lib.php b/enrol/guest/lib.php
index ac4a5cf8963..da1d2f16800 100644
--- a/enrol/guest/lib.php
+++ b/enrol/guest/lib.php
@@ -327,6 +327,22 @@ class enrol_guest_plugin extends enrol_plugin {
         }
     }
 
+    /**
+     * Add new instance of enrol plugin.
+     * @param object $course
+     * @param array instance fields
+     * @return int id of new instance, null if can not be created
+     */
+    public function add_instance($course, array $fields = NULL) {
+        $fields = (array)$fields;
+
+        if (!isset($fields['password'])) {
+            $fields['password'] = '';
+        }
+
+        return parent::add_instance($course, $fields);
+    }
+
     /**
      * Add new instance of enrol plugin with default settings.
      * @param object $course