diff --git a/src/wp-includes/widgets.php b/src/wp-includes/widgets.php
index 6f2701e5ea..0d176687fb 100644
--- a/src/wp-includes/widgets.php
+++ b/src/wp-includes/widgets.php
@@ -1262,7 +1262,7 @@ function retrieve_widgets( $theme_changed = false ) {
 	$sidebars_widgets = wp_map_sidebars_widgets( $sidebars_widgets );
 
 	// Find hidden/lost multi-widget instances.
-	$shown_widgets = call_user_func_array( 'array_merge', $sidebars_widgets );
+	$shown_widgets = array_merge( ...array_values( $sidebars_widgets ) );
 	$lost_widgets  = array_diff( $registered_widgets_ids, $shown_widgets );
 
 	foreach ( $lost_widgets as $key => $widget_id ) {