Issues with pagination on front page?

Hello!

I’m currently using the following query as suggested by the Codex on my front page:

<?php if ( get_query_var('paged') ) { $paged = get_query_var('paged'); }
elseif ( get_query_var('page') ) { $paged = get_query_var('page'); }
else { $paged = 1; } ?>
<?php $wp_query = new WP_Query(array(
    'post_type' => array('post', 'portfolio'),
    'posts_per_page' => 5,
    'paged' => $paged
)); ?>

However, this query will allow me to navigate from pages 1-3 just fine, but return 404 on page 4, even though $max_num_pages returns 7.

What am I doing wrong?