diff --git a/wp-admin/includes/template.php b/wp-admin/includes/template.php
index b57a751b3..f2560c899 100644
--- a/wp-admin/includes/template.php
+++ b/wp-admin/includes/template.php
@@ -839,11 +839,11 @@ function wp_import_upload_form( $action ) {
  * @param string $id String for use in the 'id' attribute of tags.
  * @param string $title Title of the meta box.
  * @param string $callback Function that fills the box with the desired content. The function should echo its output.
- * @param string|object $screen The screen on which to show the box (post, page, link).
- * @param string $context The context within the page where the boxes should show ('normal', 'advanced').
- * @param string $priority The priority within the context where the boxes should show ('high', 'low').
+ * @param string|object Optional. $screen The screen on which to show the box (post, page, link). Defaults to current screen.
+ * @param string $context Optional. The context within the page where the boxes should show ('normal', 'advanced').
+ * @param string $priority Optional. The priority within the context where the boxes should show ('high', 'low').
  */
-function add_meta_box($id, $title, $callback, $screen, $context = 'advanced', $priority = 'default', $callback_args=null) {
+function add_meta_box( $id, $title, $callback, $screen = null, $context = 'advanced', $priority = 'default', $callback_args = null ) {
 	global $wp_meta_boxes;
 
 	if ( empty( $screen ) )