Get featured image from post on RSS feed

I just found the right solution:

function rss_post_thumbnail($content) {

    global $post;

    if(has_post_thumbnail($post->ID)) {
        $output="<p>" . get_the_post_thumbnail($post->ID) . '</p>';
    }
    return $output . $content;
}
add_filter('the_excerpt_rss', 'rss_post_thumbnail', 20, 1);
add_filter('the_content_feed', 'rss_post_thumbnail', 20, 1);