diff --git a/src/wp-includes/rest-api/endpoints/class-wp-rest-widgets-controller.php b/src/wp-includes/rest-api/endpoints/class-wp-rest-widgets-controller.php
index 596e78aecf..267a75ffae 100644
--- a/src/wp-includes/rest-api/endpoints/class-wp-rest-widgets-controller.php
+++ b/src/wp-includes/rest-api/endpoints/class-wp-rest-widgets-controller.php
@@ -861,9 +861,9 @@ class WP_REST_Widgets_Controller extends WP_REST_Controller {
 					'type'        => 'string',
 					'context'     => array(),
 					'arg_options' => array(
-						'sanitize_callback' => static function( $string ) {
+						'sanitize_callback' => static function( $form_data ) {
 							$array = array();
-							wp_parse_str( $string, $array );
+							wp_parse_str( $form_data, $array );
 							return $array;
 						},
 					),