posts_per_page is displaying 2 less items than intended

my first question here, so I’m sorry if I do something wrong :S

I have a custom post type, called “portfolio”, and a template which I’m using to display these posts. Unfortunately, when using posts_per_page, the template is constantly displaying 2 less items than I input. Here is what I have thus far:

<?php
     $paged = (get_query_var('paged')) ? get_query_var('paged') : 1;
     $args= array('post_type' => 'portfolio', 'paged' => $paged,
            'posts_per_page' => '4');
     query_posts($args);
     if( have_posts() ) :
 ?>

It then continues into the while loop for posting the results. Any ideas on what could be causing this?