diff --git a/wp-includes/post.php b/wp-includes/post.php
index 5ebf42f89d..33a4c43314 100644
--- a/wp-includes/post.php
+++ b/wp-includes/post.php
@@ -6251,16 +6251,15 @@ function _publish_post_hook( $post_id ) {
 }
 
 /**
- * Return the post's parent's post_ID
+ * Return the post's parent post ID.
  *
  * @since 3.1.0
  *
- * @param int $post_ID
- *
+ * @param int|WP_Post $post Post ID or post object. Defaults to global $post.
  * @return int|false Post parent ID, otherwise false.
  */
-function wp_get_post_parent_id( $post_ID ) {
-	$post = get_post( $post_ID );
+function wp_get_post_parent_id( $post ) {
+	$post = get_post( $post );
 	if ( ! $post || is_wp_error( $post ) ) {
 		return false;
 	}
diff --git a/wp-includes/version.php b/wp-includes/version.php
index e9eb1a1d1e..eccdce38f3 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.0-alpha-42396';
+$wp_version = '5.0-alpha-42397';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.