diff --git a/core/lib/Drupal/Core/Extension/module.api.php b/core/lib/Drupal/Core/Extension/module.api.php
index 8dc2e40..2cfbd80 100644
--- a/core/lib/Drupal/Core/Extension/module.api.php
+++ b/core/lib/Drupal/Core/Extension/module.api.php
@@ -667,8 +667,12 @@ function hook_update_N(&$sandbox) {
  * These updates are executed after all hook_update_N() implementations. At this
  * stage Drupal is already fully repaired so you can use any API as you wish.
  *
- * Note: In contrast to hook_update_N() there is no enforced order, so you can
- * also use machine names for the name of those updates.
+ * NAME can be arbitrary machine names. In contrast to hook_update_N() the order
+ * of functions in the file is the only thing which ensures the execution order
+ * of those functions.
+ *
+ * Drupal also ensures to not execute the same hook_post_update_NAME() function
+ * twice.
  *
  * @param array $sandbox
  *   Stores information for batch updates. See above for more information.