Pretty permalinks for custom post type archives

Currently my custom post type archives are can be accessed by either

mysite/mycustomposttype

or

mysite/?post_type=mycustomposttype

This is not good in terms of duplicate content on search engines etc.

Permalinks are operative using Permalink settings: /%year%/%postname%/

Individual CPT are fine.

Seems like CPT archives are not getting the proper rewrite treatment. So my question – is something broken or do they require rewrites to be set up manually elsewhere?

add_action( 'init', 'create_my_post_types' );
function create_my_post_types() {
register_post_type( 'mycustomposttype',
    array(
        'labels' => array(
            'name' => __( 'Mycustomposttype' ),
            'singular_name' => __( 'Mycustomposttype' ),
            'add_new' => __( 'Add New Mycustomposttype Listing' ),
            'add_new_item' => __( 'Add New Mycustomposttype Listing' ),
            'edit' => __( 'Edit' ),
            'edit_item' => __( 'Edit Mycustomposttype Listing' ),
            'new_item' => __( 'New Mycustomposttype Listing' ),
            'view' => __( 'View Mycustomposttype' ),
            'view_item' => __( 'View Mycustomposttype Listing' ),
            'search_items' => __( 'Search Mycustomposttype Listings' ),
            'not_found' => __( 'No Mycustomposttype Listing found' ),
            'not_found_in_trash' => __( 'No Mycustomposttype Listing found in Trash' )
        ),
        'description' => __( 'Mycustomposttype' ),
        'public' => true,
        'show_ui' => true,
        'publicly_queryable' => true,
        'exclude_from_search' => false,
        'menu_position' => 5,
        'hierarchical' => true,
        'query_var' => true,
        'supports' => array( 'title', 'editor', 'comments', 'trackbacks', 'revisions', 'author', 'excerpt', 'custom-fields', 'page-attributes', 'thumbnail', 'post-formats' ),
        'rewrite' => array( 'slug' => 'mycustomposttype', 'with_front' => false ),
        'taxonomies' => array( 'post_tag','category','stuff','other-stuff' ),
        'has_archive' => true,
        'show_in_nav_menus' => true,
        'can_export' => true,

    )
);