diff --git a/lib/class-wp-rest-block-renderer-controller.php b/lib/class-wp-rest-block-renderer-controller.php
index 3ecf25de44930..b9839f080376a 100644
--- a/lib/class-wp-rest-block-renderer-controller.php
+++ b/lib/class-wp-rest-block-renderer-controller.php
@@ -59,6 +59,7 @@ public function register_routes() {
 								'type'                 => 'object',
 								'additionalProperties' => false,
 								'properties'           => $block_type->get_attributes(),
+								'default'              => array(),
 							),
 							'post_id'    => array(
 								'description' => __( 'ID of the post context.', 'gutenberg' ),