Index: wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php
===================================================================
--- wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php	(revision 40058)
+++ wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php	(working copy)
@@ -1289,7 +1289,9 @@
 		// Can we read the parent if we're inheriting?
 		if ( 'inherit' === $post->post_status && $post->post_parent > 0 ) {
 			$parent = get_post( $post->post_parent );
-			return $this->check_read_permission( $parent );
+			if ( $parent ) {
+				return $this->check_read_permission( $parent );
+			}
 		}
 
 		/*