diff --git a/src/wp-includes/revision.php b/src/wp-includes/revision.php
index 7bb7be1cb2..e99139df60 100644
--- a/src/wp-includes/revision.php
+++ b/src/wp-includes/revision.php
@@ -227,6 +227,8 @@ function wp_save_post_revision( $post_id ) {
  *
  * @since 2.6.0
  *
+ * @global wpdb $wpdb WordPress database abstraction object.
+ *
  * @param int $post_id The post ID.
  * @param int $user_id Optional The post author ID.
  * @return WP_Post|false The autosaved data or false on failure or when no autosave exists.