diff --git a/src/wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php b/src/wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php
index 0ab54a3a0d384..a3a884b862e14 100644
--- a/src/wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php
+++ b/src/wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php
@@ -766,10 +766,10 @@ public function create_item( $request ) {
 			 */
 			$prepared_post->post_name = wp_unique_post_slug(
 				$prepared_post->post_name,
-				$prepared_post->id,
+				isset( $prepared_post->ID ) ? $prepared_post->ID : 0,
 				'publish',
 				$prepared_post->post_type,
-				$prepared_post->post_parent
+				isset( $prepared_post->post_parent ) ? $prepared_post->post_parent : 0
 			);
 		}