diff --git a/src/wp-includes/class-wp-theme-json.php b/src/wp-includes/class-wp-theme-json.php
index 9fea12a8d3e99..4826de8648acd 100644
--- a/src/wp-includes/class-wp-theme-json.php
+++ b/src/wp-includes/class-wp-theme-json.php
@@ -344,6 +344,7 @@ class WP_Theme_JSON {
 	 * @since 6.3.0 Added support for `typography.textColumns`, removed `layout.definitions`.
 	 * @since 6.4.0 Added support for `layout.allowEditing`, `background.backgroundImage`,
 	 *              `typography.writingMode`, `lightbox.enabled` and `lightbox.allowEditing`.
+	 * @since 6.5.0 Added support for `layout.allowCustomContentAndWideSize`.
 	 * @var array
 	 */
 	const VALID_SETTINGS = array(
@@ -380,9 +381,10 @@ class WP_Theme_JSON {
 			'minHeight' => null,
 		),
 		'layout'                        => array(
-			'contentSize'  => null,
-			'wideSize'     => null,
-			'allowEditing' => null,
+			'contentSize'                   => null,
+			'wideSize'                      => null,
+			'allowEditing'                  => null,
+			'allowCustomContentAndWideSize' => null,
 		),
 		'lightbox'                      => array(
 			'enabled'      => null,