diff --git a/wp-includes/sitemaps/providers/class-wp-sitemaps-posts.php b/wp-includes/sitemaps/providers/class-wp-sitemaps-posts.php
index c9d982ddce..701d170a6a 100644
--- a/wp-includes/sitemaps/providers/class-wp-sitemaps-posts.php
+++ b/wp-includes/sitemaps/providers/class-wp-sitemaps-posts.php
@@ -148,15 +148,20 @@ class WP_Sitemaps_Posts extends WP_Sitemaps_Provider {
 	 * Gets the max number of pages available for the object type.
 	 *
 	 * @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 string $post_type Optional. Post type name. Default empty.
+	 * @param string $object_subtype Optional. Post type name. Default empty.
 	 * @return int Total number of pages.
 	 */
-	public function get_max_num_pages( $post_type = '' ) {
-		if ( empty( $post_type ) ) {
+	public function get_max_num_pages( $object_subtype = '' ) {
+		if ( empty( $object_subtype ) ) {
 			return 0;
 		}
 
+		// Restores the more descriptive, specific name for use within this method.
+		$post_type = $object_subtype;
+
 		/**
 		 * Filters the max number of pages before it is generated.
 		 *
diff --git a/wp-includes/sitemaps/providers/class-wp-sitemaps-taxonomies.php b/wp-includes/sitemaps/providers/class-wp-sitemaps-taxonomies.php
index f5b6bb631a..636815397e 100644
--- a/wp-includes/sitemaps/providers/class-wp-sitemaps-taxonomies.php
+++ b/wp-includes/sitemaps/providers/class-wp-sitemaps-taxonomies.php
@@ -134,15 +134,20 @@ class WP_Sitemaps_Taxonomies extends WP_Sitemaps_Provider {
 	 * Gets the max number of pages available for the object type.
 	 *
 	 * @since 5.5.0
+	 * @since 5.9.0 Renamed `$taxonomy` to `$object_subtype` to match parent class
+	 *              for PHP 8 named parameter support.
 	 *
-	 * @param string $taxonomy Taxonomy name.
+	 * @param string $object_subtype Optional. Taxonomy name. Default empty.
 	 * @return int Total number of pages.
 	 */
-	public function get_max_num_pages( $taxonomy = '' ) {
-		if ( empty( $taxonomy ) ) {
+	public function get_max_num_pages( $object_subtype = '' ) {
+		if ( empty( $object_subtype ) ) {
 			return 0;
 		}
 
+		// Restores the more descriptive, specific name for use within this method.
+		$taxonomy = $object_subtype;
+
 		/**
 		 * Filters the max number of pages before it is generated.
 		 *
diff --git a/wp-includes/version.php b/wp-includes/version.php
index b4a0d52faf..89812b9a99 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.9-alpha-51787';
+$wp_version = '5.9-alpha-51788';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.