diff --git a/lib/classes/task/manager.php b/lib/classes/task/manager.php
index 95cbcfcdf56..60a5240baac 100644
--- a/lib/classes/task/manager.php
+++ b/lib/classes/task/manager.php
@@ -421,8 +421,16 @@ class manager {
 
         foreach ($records as $record) {
 
-            if ($lock = $cronlockfactory->get_lock('adhoc_' . $record->id, 10)) {
+            if ($lock = $cronlockfactory->get_lock('adhoc_' . $record->id, 0)) {
                 $classname = '\\' . $record->classname;
+
+                // Safety check, see if the task has been already processed by another cron run.
+                $record = $DB->get_record('task_adhoc', array('id' => $record->id));
+                if (!$record) {
+                    $lock->release();
+                    continue;
+                }
+
                 $task = self::adhoc_task_from_record($record);
                 // Safety check in case the task in the DB does not match a real class (maybe something was uninstalled).
                 if (!$task) {
@@ -472,7 +480,7 @@ class manager {
 
         foreach ($records as $record) {
 
-            if ($lock = $cronlockfactory->get_lock(($record->classname), 10)) {
+            if ($lock = $cronlockfactory->get_lock(($record->classname), 0)) {
                 $classname = '\\' . $record->classname;
                 $task = self::scheduled_task_from_record($record);
                 // Safety check in case the task in the DB does not match a real class (maybe something was uninstalled).