WordPress : Hack to give a custom posts_per_page value for a custom post type

WP : custom posts_per_page for custom post type

//This code should be added in the plugin that manages the custom post type or in the functions.php of you theme

add_filter('request', 'hack_pagination');//Register the filter

/** 
* Hack to give a custom posts_per_page value for a custom post type
* @param string $query_string automatically given by the filter
*/
function hack_pagination($query_string){
  if($query_string['post_type']=='MY_CUSTOM_POST_TYPE' && !is_single() && !is_admin()) {
    $query_string['posts_per_page'] = 2;//Number of posts I want in archive
  }
  return $query_string;
}