Get image attachments ordered by sorter

I’m using the array below with get_posts() to get the image attachments.

// Get images for this post
    $args = array(
      'post_type' => 'attachment',
      'numberposts' => -1,
      'post_status' => null,
      'post_mime_type' => 'image',
      'post_parent' => $post->ID
      );

How do I order them on the ‘order’ entered in the gallery?

Thanks!