diff --git a/lib/classes/task/adhoc_task.php b/lib/classes/task/adhoc_task.php
index 69c7db08ca9..d537dd9f76e 100644
--- a/lib/classes/task/adhoc_task.php
+++ b/lib/classes/task/adhoc_task.php
@@ -46,8 +46,8 @@ abstract class adhoc_task extends task_base {
     /** @var \core\lock\lock The concurrency task lock for this task. */
     private $concurrencylock = null;
 
-    /** @var integer|null $attemptsavailable - The remaining attempts of the task, or null for unlimited. */
-    private $attemptsavailable = null;
+    /** @var int $attemptsavailable - The remaining attempts of the task. */
+    private $attemptsavailable = 12;
 
     /**
      * Provide default implementation of the task name for backward compatibility. Extending classes are expected to implement
@@ -178,18 +178,18 @@ abstract class adhoc_task extends task_base {
     /**
      * Set the remaining attempts of the task.
      *
-     * @param int|null $attemptsavailable Number of the remaining attempts of the task, or null for unlimited.
+     * @param int $attemptsavailable Number of the remaining attempts of the task.
      */
-    public function set_attempts_available(?int $attemptsavailable): void {
+    public function set_attempts_available(int $attemptsavailable): void {
         $this->attemptsavailable = $attemptsavailable;
     }
 
     /**
      * Get the remaining attempts of the task.
      *
-     * @return int|null Number of the remaining attempts of the task, or null for unlimited.
+     * @return int Number of the remaining attempts of the task.
      */
-    public function get_attempts_available(): ?int {
+    public function get_attempts_available(): int {
         return $this->attemptsavailable;
     }
 
diff --git a/lib/classes/task/manager.php b/lib/classes/task/manager.php
index 7d70d8014ea..1a036c814bf 100644
--- a/lib/classes/task/manager.php
+++ b/lib/classes/task/manager.php
@@ -56,11 +56,6 @@ class manager {
      */
     const ADHOC_TASK_FAILED_RETENTION = 4 * WEEKSECS;
 
-    /**
-     * @var int Used for max retry.
-     */
-    const MAX_RETRY = 9;
-
     /**
      * @var ?task_base $runningtask Used to tell what is the current running task in this process.
      */
@@ -261,7 +256,7 @@ class manager {
         }
 
         // Check if the task is allowed to be retried or not.
-        $record->attemptsavailable = $task->retry_until_success() ? self::MAX_RETRY : 1;
+        $record->attemptsavailable = $task->retry_until_success() ? $record->attemptsavailable : 1;
         // Set the time the task was created.
         $record->timecreated = time();
 
diff --git a/lib/tests/task/adhoc_task_test.php b/lib/tests/task/adhoc_task_test.php
index fdef01e05f4..f3e93da3549 100644
--- a/lib/tests/task/adhoc_task_test.php
+++ b/lib/tests/task/adhoc_task_test.php
@@ -136,6 +136,32 @@ final class adhoc_task_test extends \advanced_testcase {
         $this->assertNull(manager::get_next_adhoc_task($now));
     }
 
+    /**
+     * Test that failed tasks eventually hit the maximum delay.
+     *
+     * @covers \core\task\adhoc_task
+     */
+    public function test_get_next_adhoc_task_maximum_fail_delay(): void {
+        $this->resetAfterTest(true);
+
+        $now = time();
+
+        // Create an adhoc task.
+        $task = new adhoc_test_task();
+        $attemptsavailable = $task->get_attempts_available();
+        manager::queue_adhoc_task($task);
+
+        // Exhaust all attempts available.
+        for ($x = 0; $x < $attemptsavailable; $x++) {
+            $delay = $task->get_fail_delay() * 2;
+            $task = manager::get_next_adhoc_task($now + $delay);
+            $task->execute();
+            manager::adhoc_task_failed($task);
+        }
+        // Check that the fail delay is now set to 24 hours (the maximum amount of times).
+        $this->assertEquals(DAYSECS, $task->get_fail_delay());
+    }
+
     /**
      * Test adhoc task failure retry backoff.
      */
@@ -148,13 +174,13 @@ final class adhoc_task_test extends \advanced_testcase {
         $task = new adhoc_test_task();
         $taskid1 = manager::queue_adhoc_task(task: $task);
 
-        // This is a normal task, so it should have unlimited attempts. The remaining available attempts should be null.
+        // This is a normal task, so it should have limited attempts.
         $attemptsavailable = $DB->get_field(
             table: 'task_adhoc',
             return: 'attemptsavailable',
             conditions: ['id' => $taskid1]
         );
-        $this->assertEquals(expected: manager::MAX_RETRY, actual: $attemptsavailable);
+        $this->assertEquals(expected: 12, actual: $attemptsavailable);
 
         // Get the task from the scheduler, execute it, and mark it as failed.
         $task = manager::get_next_adhoc_task(timestart: $now);
@@ -162,13 +188,13 @@ final class adhoc_task_test extends \advanced_testcase {
         $task->execute();
         manager::adhoc_task_failed(task: $task);
 
-        // This is a normal task, so it should have unlimited attempts. The remaining available attempts should be null.
+        // Now that the task has failed, there should be one less attempt available.
         $attemptsavailable = $DB->get_field(
             table: 'task_adhoc',
             return: 'attemptsavailable',
             conditions: ['id' => $taskid1]
         );
-        $this->assertEquals(expected: manager::MAX_RETRY - 1, actual: $attemptsavailable);
+        $this->assertEquals(expected: 12 - 1, actual: $attemptsavailable);
 
         // Create a no-retry adhoc task.
         $now = time();