Update (not show!) a feed after publish a custom post type

Hi,
surfing in the web I found this useful snippet to show custom post types in the feed and in the homepage. But unfortunately when I publish a new custom post type it doesn’t update the feed and it update it only after I publish a normal post, and then I can see both the post both the custom post type I previously published.
So what have I to edit in this script??

add_filter( 'pre_get_posts', 'my_get_posts' );
function my_get_posts( $query ) {

	if ( ( is_home() && false == $query->query_vars['suppress_filters'] ) || is_feed() )
		$query->set( 'post_type', array( 'post', 'custom_post') );

	return $query;
}

Thanks all!