diff --git a/wp-admin/includes/template.php b/wp-admin/includes/template.php
index 06da772d6d..61d7465a6e 100644
--- a/wp-admin/includes/template.php
+++ b/wp-admin/includes/template.php
@@ -1806,7 +1806,7 @@ add_action( 'admin_enqueue_scripts', array( 'WP_Internal_Pointers', 'enqueue_scr
  * @return WP_Screen Screen object.
  */
 function convert_to_screen( $hook_name ) {
-	if ( ! is_admin() ) {
+	if ( ! class_exists( 'WP_Screen' ) ) {
 		_doing_it_wrong( 'convert_to_screen(), add_meta_box()', __( "Likely direct inclusion of wp-admin/includes/template.php in order to use add_meta_box(). This is very wrong. Hook the add_meta_box() call into the add_meta_boxes action instead." ), '3.3' );
 		return (object) array( 'id' => '_invalid', 'base' => '_are_belong_to_us' );
 	}