diff --git a/src/wp-includes/post.php b/src/wp-includes/post.php
index b58b7d72d4..6e7870ba5e 100644
--- a/src/wp-includes/post.php
+++ b/src/wp-includes/post.php
@@ -452,6 +452,7 @@ function create_initial_post_types() {
 			'label'        => __( 'Global Styles' ),
 			'description'  => 'CPT to store user design tokens',
 			'public'       => false,
+			'_builtin'     => true, /* internal use only. don't use this when registering your own post type. */
 			'show_ui'      => false,
 			'show_in_rest' => false,
 			'rewrite'      => false,