diff --git a/src/wp-includes/widgets.php b/src/wp-includes/widgets.php
index 1f17a35808..433234260d 100644
--- a/src/wp-includes/widgets.php
+++ b/src/wp-includes/widgets.php
@@ -1370,6 +1370,8 @@ function retrieve_widgets( $theme_changed = false ) {
  * @since 4.9.0
  * @since 4.9.2 Always tries to restore widget assignments from previous data, not just if sidebars needed mapping.
  *
+ * @global array $wp_registered_sidebars The registered sidebars.
+ *
  * @param array $existing_sidebars_widgets List of sidebars and their widget instance IDs.
  * @return array Mapped sidebars widgets.
  */