diff --git a/wp-includes/sitemaps/providers/class-wp-sitemaps-posts.php b/wp-includes/sitemaps/providers/class-wp-sitemaps-posts.php
index 56acfb7697..c9d982ddce 100644
--- a/wp-includes/sitemaps/providers/class-wp-sitemaps-posts.php
+++ b/wp-includes/sitemaps/providers/class-wp-sitemaps-posts.php
@@ -53,12 +53,18 @@ class WP_Sitemaps_Posts extends WP_Sitemaps_Provider {
 	 * Gets a URL list for a post type sitemap.
 	 *
 	 * @since 5.5.0
+	 * @since 5.9.0 Renamed `$post_type` to `$object_subtype` to match parent class
+	 *              for PHP 8 named parameter support.
+	 *
+	 * @param int    $page_num       Page of results.
+	 * @param string $object_subtype Optional. Post type name. Default empty.
 	 *
-	 * @param int    $page_num  Page of results.
-	 * @param string $post_type Optional. Post type name. Default empty.
 	 * @return array Array of URLs for a sitemap.
 	 */
-	public function get_url_list( $page_num, $post_type = '' ) {
+	public function get_url_list( $page_num, $object_subtype = '' ) {
+		// Restores the more descriptive, specific name for use within this method.
+		$post_type = $object_subtype;
+
 		// Bail early if the queried post type is not supported.
 		$supported_types = $this->get_object_subtypes();
 
diff --git a/wp-includes/sitemaps/providers/class-wp-sitemaps-taxonomies.php b/wp-includes/sitemaps/providers/class-wp-sitemaps-taxonomies.php
index e8fcc6d5ab..f5b6bb631a 100644
--- a/wp-includes/sitemaps/providers/class-wp-sitemaps-taxonomies.php
+++ b/wp-includes/sitemaps/providers/class-wp-sitemaps-taxonomies.php
@@ -51,12 +51,16 @@ class WP_Sitemaps_Taxonomies extends WP_Sitemaps_Provider {
 	 * Gets a URL list for a taxonomy sitemap.
 	 *
 	 * @since 5.5.0
+	 * @since 5.9.0 Renamed `$taxonomy` to `$object_subtype` to match parent class
+	 *              for PHP 8 named parameter support.
 	 *
-	 * @param int    $page_num Page of results.
-	 * @param string $taxonomy Optional. Taxonomy name. Default empty.
+	 * @param int    $page_num       Page of results.
+	 * @param string $object_subtype Optional. Taxonomy name. Default empty.
 	 * @return array Array of URLs for a sitemap.
 	 */
-	public function get_url_list( $page_num, $taxonomy = '' ) {
+	public function get_url_list( $page_num, $object_subtype = '' ) {
+		// Restores the more descriptive, specific name for use within this method.
+		$taxonomy        = $object_subtype;
 		$supported_types = $this->get_object_subtypes();
 
 		// Bail early if the queried taxonomy is not supported.
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 11d347449b..b4a0d52faf 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.9-alpha-51786';
+$wp_version = '5.9-alpha-51787';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.