diff --git a/core/includes/install.inc b/core/includes/install.inc
index 3593725..98f5a99 100644
--- a/core/includes/install.inc
+++ b/core/includes/install.inc
@@ -1025,6 +1025,9 @@ function drupal_check_module($module) {
         if (isset($requirement['value']) && $requirement['value']) {
           $message .= ' (' . t('Currently using !item !version', array('!item' => $requirement['title'], '!version' => $requirement['value'])) . ')';
         }
+        // Make sure to mark the message string as secure.
+        // The string was previously checked as safe or escaped properly with
+        // SafeMarkup::escape() method.
         drupal_set_message(SafeMarkup::set($message), 'error');
       }
     }