diff --git a/cache/upgrade.txt b/cache/upgrade.txt
index 768f66716ac..f367cad72b3 100644
--- a/cache/upgrade.txt
+++ b/cache/upgrade.txt
@@ -3,6 +3,8 @@ Information provided here is intended especially for developers.
 
 === 4.0 ===
 * The function supports_recursion() from the lock_factory interface has been deprecated including the related implementations.
+* The function extend_lock() from the lock_factory interface has been deprecated without replacement including the related
+  implementations.
 
 === 3.9 ===
 * The record_cache_hit/miss/set methods now take a cache_store instead of a cache_definition object
diff --git a/lib/classes/lock/db_record_lock_factory.php b/lib/classes/lock/db_record_lock_factory.php
index 11ec1a187a2..4dfec49c4de 100644
--- a/lib/classes/lock/db_record_lock_factory.php
+++ b/lib/classes/lock/db_record_lock_factory.php
@@ -191,11 +191,16 @@ class db_record_lock_factory implements lock_factory {
 
     /**
      * Extend a lock that was previously obtained with @lock.
+     *
+     * @deprecated since Moodle 4.0.
      * @param lock $lock - a lock obtained from this factory.
      * @param int $maxlifetime - the new lifetime for the lock (in seconds).
      * @return boolean - true if the lock was extended.
      */
     public function extend_lock(lock $lock, $maxlifetime = 86400) {
+        debugging('The function extend_lock() is deprecated, please do not use it anymore.',
+            DEBUG_DEVELOPER);
+
         $now = time();
         $expires = $now + $maxlifetime;
         $params = array('expires' => $expires,
diff --git a/lib/classes/lock/file_lock_factory.php b/lib/classes/lock/file_lock_factory.php
index d719cd9112c..b7716399007 100644
--- a/lib/classes/lock/file_lock_factory.php
+++ b/lib/classes/lock/file_lock_factory.php
@@ -192,11 +192,15 @@ class file_lock_factory implements lock_factory {
 
     /**
      * Extend a lock that was previously obtained with @lock.
+     *
+     * @deprecated since Moodle 4.0.
      * @param lock $lock - not used
      * @param int $maxlifetime - not used
      * @return boolean - true if the lock was extended.
      */
     public function extend_lock(lock $lock, $maxlifetime = 86400) {
+        debugging('The function extend_lock() is deprecated, please do not use it anymore.',
+            DEBUG_DEVELOPER);
         // Not supported by this factory.
         return false;
     }
diff --git a/lib/classes/lock/installation_lock_factory.php b/lib/classes/lock/installation_lock_factory.php
index 36ebdd951d1..0874cedc610 100644
--- a/lib/classes/lock/installation_lock_factory.php
+++ b/lib/classes/lock/installation_lock_factory.php
@@ -118,11 +118,14 @@ class installation_lock_factory implements lock_factory {
     /**
      * Extend a lock that was previously obtained with @lock.
      *
+     * @deprecated since Moodle 4.0.
      * @param lock $lock - not used
      * @param int $maxlifetime - not used
      * @return boolean - true if the lock was extended.
      */
     public function extend_lock(lock $lock, $maxlifetime = 86400) {
+        debugging('The function extend_lock() is deprecated, please do not use it anymore.',
+            DEBUG_DEVELOPER);
         // Not supported by this factory.
         return false;
     }
diff --git a/lib/classes/lock/lock_factory.php b/lib/classes/lock/lock_factory.php
index 9d3303e0e2a..c0d32b0a1ff 100644
--- a/lib/classes/lock/lock_factory.php
+++ b/lib/classes/lock/lock_factory.php
@@ -99,6 +99,7 @@ interface lock_factory {
     /**
      * Extend the timeout on a held lock.
      *
+     * @deprecated since Moodle 4.0.
      * @param lock $lock - lock obtained from this factory
      * @param int $maxlifetime - new max time to hold the lock
      * @return boolean - True if the lock was extended.
diff --git a/lib/classes/lock/mysql_lock_factory.php b/lib/classes/lock/mysql_lock_factory.php
index 5efb2927732..753741b4655 100644
--- a/lib/classes/lock/mysql_lock_factory.php
+++ b/lib/classes/lock/mysql_lock_factory.php
@@ -168,11 +168,15 @@ class mysql_lock_factory implements lock_factory {
 
     /**
      * Extend a lock that was previously obtained with @lock.
+     *
+     * @deprecated since Moodle 4.0.
      * @param lock $lock - a lock obtained from this factory.
      * @param int $maxlifetime - the new lifetime for the lock (in seconds).
      * @return boolean - true if the lock was extended.
      */
     public function extend_lock(lock $lock, $maxlifetime = 86400) {
+        debugging('The function extend_lock() is deprecated, please do not use it anymore.',
+            DEBUG_DEVELOPER);
         // Not supported by this factory.
         return false;
     }
diff --git a/lib/classes/lock/postgres_lock_factory.php b/lib/classes/lock/postgres_lock_factory.php
index c100acb934c..1d2ccf6159e 100644
--- a/lib/classes/lock/postgres_lock_factory.php
+++ b/lib/classes/lock/postgres_lock_factory.php
@@ -198,11 +198,15 @@ class postgres_lock_factory implements lock_factory {
 
     /**
      * Extend a lock that was previously obtained with @lock.
+     *
+     * @deprecated since Moodle 4.0.
      * @param lock $lock - a lock obtained from this factory.
      * @param int $maxlifetime - the new lifetime for the lock (in seconds).
      * @return boolean - true if the lock was extended.
      */
     public function extend_lock(lock $lock, $maxlifetime = 86400) {
+        debugging('The function extend_lock() is deprecated, please do not use it anymore.',
+            DEBUG_DEVELOPER);
         // Not supported by this factory.
         return false;
     }