diff --git a/lib/class-wp-rest-block-types-controller.php b/lib/class-wp-rest-block-types-controller.php
index e73dd74783956..c90d6366cc1f4 100644
--- a/lib/class-wp-rest-block-types-controller.php
+++ b/lib/class-wp-rest-block-types-controller.php
@@ -431,7 +431,7 @@ public function get_item_schema() {
 				),
 				'parent'        => array(
 					'description' => __( 'Parent blocks.', 'gutenberg' ),
-					'type'        => 'array',
+					'type'        => array( 'null', 'array' ),
 					'items'       => array(
 						'type' => 'string',
 					),