diff --git a/src/wp-includes/class-wp-customize-manager.php b/src/wp-includes/class-wp-customize-manager.php
index 79f2b3eab3..252365c763 100644
--- a/src/wp-includes/class-wp-customize-manager.php
+++ b/src/wp-includes/class-wp-customize-manager.php
@@ -493,12 +493,28 @@ final class WP_Customize_Manager {
 		return '_default_wp_die_handler';
 	}
 
+	/**
+	 * Redirects to 404 when changeset UUID does not exists for unauthenticated users.
+	 *
+	 * @since 5.6.0
+	 *
+	 * @param bool     $bypass Pass-through of the pre_handle_404 filter value.
+	 * @param WP_Query $query  The WP_Query object.
+	 * @return bool Bypass value.
+	 */
+	public function customize_changeset_preview_redirect( $bypass, $query ) {
+		$query->set_404();
+		status_header( 404 );
+		return $bypass;
+	}
+
 	/**
 	 * Start preview and customize theme.
 	 *
 	 * Check if customize query variable exist. Init filters to filter the current theme.
 	 *
 	 * @since 3.4.0
+	 * @since 5.6.0 Redirects to 404 when changeset UUID does not exists for unauthenticated users.
 	 *
 	 * @global string $pagenow
 	 */
@@ -548,7 +564,13 @@ final class WP_Customize_Manager {
 		 * then send unauthenticated code to prompt re-auth.
 		 */
 		if ( ! current_user_can( 'customize' ) && ! $this->changeset_post_id() ) {
-			$this->wp_die( $this->messenger_channel ? 0 : -1, __( 'Non-existent changeset UUID.' ) );
+			// As this is a preview page sending noindex in headers.
+			if ( ! headers_sent() ) {
+				nocache_headers();
+				header( 'X-Robots: noindex, nofollow, noarchive' );
+			}
+			add_action( 'wp_head', 'wp_no_robots' );
+			add_filter( 'pre_handle_404', array( $this, 'customize_changeset_preview_redirect' ), 1, 2 );
 		}
 
 		if ( ! headers_sent() ) {