diff --git src/wp-includes/class-wp-customize-nav-menus.php src/wp-includes/class-wp-customize-nav-menus.php
index 28e8196917..955ce1a82f 100644
--- src/wp-includes/class-wp-customize-nav-menus.php
+++ src/wp-includes/class-wp-customize-nav-menus.php
@@ -786,7 +786,7 @@ final class WP_Customize_Nav_Menus {
 	 * @return WP_Post|WP_Error Inserted auto-draft post object or error.
 	 */
 	public function insert_auto_draft_post( $postarr ) {
-		if ( ! isset( $postarr['post_type'] ) || ! post_type_exists( $postarr['post_type'] )  ) {
+		if ( ! isset( $postarr['post_type'] )  ) {
 			return new WP_Error( 'unknown_post_type', __( 'Invalid post type.' ) );
 		}
 		if ( empty( $postarr['post_title'] ) ) {