diff --git a/includes/common.inc b/includes/common.inc
index ceac115..81536df 100644
--- a/includes/common.inc
+++ b/includes/common.inc
@@ -5308,8 +5308,8 @@ function drupal_page_set_cache() {
  *
  * Do not call this function from a test. Use $this->cronRun() instead.
  *
- * @return
- *   TRUE if cron ran successfully.
+ * @return bool
+ *   TRUE if cron ran successfully, FALSE if a lock (it does not allow to re-run while its already running) could not be acquired.
  */
 function drupal_cron_run() {
   // Allow execution to continue even if the request gets canceled.