diff --git a/core/modules/update/update.module b/core/modules/update/update.module
index 4aed1ef..fe04feb 100644
--- a/core/modules/update/update.module
+++ b/core/modules/update/update.module
@@ -459,6 +459,11 @@ function update_mail($key, &$message, $params) {
  * site-wide status report at admin/reports/status and in the body of the
  * notification email messages generated by update_cron().
  *
+ * @todo With https://www.drupal.org/node/2505499 return a render array to be
+ *   used in hook_requirements. This would allow [#markup => $text] to be passed
+ *   back and \Drupal\Core\Render\Renderer\renderPlain() can be used for the
+ *   email message.
+ *
  * @param $msg_type
  *   String to indicate what kind of message to generate. Can be either 'core'
  *   or 'contrib'.