diff --git a/lib/classes/task/send_failed_login_notifications_task.php b/lib/classes/task/send_failed_login_notifications_task.php
index 7791fcf8fc5..3fbe3b99f1d 100644
--- a/lib/classes/task/send_failed_login_notifications_task.php
+++ b/lib/classes/task/send_failed_login_notifications_task.php
@@ -28,6 +28,9 @@ namespace core\task;
  */
 class send_failed_login_notifications_task extends scheduled_task {
 
+    /** The maximum time period to look back (30 days = 30 * 24 * 3600) */
+    const NOTIFY_MAXIMUM_TIME = 2592000;
+
     /**
      * Get a descriptive name for this task (shown to admins).
      *
@@ -50,8 +53,10 @@ class send_failed_login_notifications_task extends scheduled_task {
 
         $recip = get_users_from_config($CFG->notifyloginfailures, 'moodle/site:config');
 
-        if (empty($CFG->lastnotifyfailure)) {
-            $CFG->lastnotifyfailure = 0;
+        // Do not look back more than 1 month to avoid crashes due to huge number of records.
+        $maximumlastnotifytime = time() - self::NOTIFY_MAXIMUM_TIME;
+        if (empty($CFG->lastnotifyfailure) || ($CFG->lastnotifyfailure < $maximumlastnotifytime)) {
+            $CFG->lastnotifyfailure = $maximumlastnotifytime;
         }
 
         // If it has been less than an hour, or if there are no recipients, don't execute.