Custom Post Type Templates not working

I’m working with a custom post type called ‘portfolio’, and I’m trying to use custom post type templates to create an archive page and a single page for the post type. However, I’m unable to get either to work. When I visit the url for a post using the post type, I get the 404 page.

The post type is called ‘portfolio’, and the files are called ‘single-portfolio.php’ and ‘archive-portfolio.php’. I have flushed the permalink settings (rewrite rules). I’m running XAMPP on a Mac.

Code:

add_action('init', 'portfolio_register');    

function portfolio_register() {
    $args = array(
        'label' => __('Portfolio'),
        'singular_label' => __('Projekt'),
        'public' => true,
        'show_ui' => true,
        'capability_type' => 'post',
        'hierarchical' => false,
        'has_archive' => true,
        'rewrite' => true,
        'supports' => array('title', 'editor', 'thumbnail')
       );    

    register_post_type( 'portfolio' , $args );
}