diff --git a/wp-includes/class-wp-theme.php b/wp-includes/class-wp-theme.php
index a3c996e59f..d0607528b5 100644
--- a/wp-includes/class-wp-theme.php
+++ b/wp-includes/class-wp-theme.php
@@ -556,6 +556,7 @@ final class WP_Theme implements ArrayAccess {
 	 * @param mixed $offset
 	 * @param mixed $value
 	 */
+	#[ReturnTypeWillChange]
 	public function offsetSet( $offset, $value ) {}
 
 	/**
@@ -565,6 +566,7 @@ final class WP_Theme implements ArrayAccess {
 	 *
 	 * @param mixed $offset
 	 */
+	#[ReturnTypeWillChange]
 	public function offsetUnset( $offset ) {}
 
 	/**
@@ -575,6 +577,7 @@ final class WP_Theme implements ArrayAccess {
 	 * @param mixed $offset
 	 * @return bool
 	 */
+	#[ReturnTypeWillChange]
 	public function offsetExists( $offset ) {
 		static $keys = array(
 			'Name',
@@ -616,6 +619,7 @@ final class WP_Theme implements ArrayAccess {
 	 * @param mixed $offset
 	 * @return mixed
 	 */
+	#[ReturnTypeWillChange]
 	public function offsetGet( $offset ) {
 		switch ( $offset ) {
 			case 'Name':
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 6cd0bac08c..dc3e5a876b 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.9-alpha-51528';
+$wp_version = '5.9-alpha-51529';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.