diff --git a/includes/common.inc b/includes/common.inc
index ceac115..fc8a903 100644
--- a/includes/common.inc
+++ b/includes/common.inc
@@ -5309,7 +5309,8 @@ function drupal_page_set_cache() {
  * Do not call this function from a test. Use $this->cronRun() instead.
  *
  * @return
- *   TRUE if cron ran successfully.
+ *   TRUE if cron ran successfully, or FALSE if a lock could not be acquired
+ *   i.e. it does not allow to re-run while its already running.
  */
 function drupal_cron_run() {
   // Allow execution to continue even if the request gets canceled.