query_posts() – problem with “s” parameter

I’m trying to create a search page for a custom post type. This is the code I’m using:

$s = $_GET['s'];
$args = array(
        'post_type' => 'companies',
        's'         => $s
);
query_posts($args);

if ( have_posts() ) :
....results.....
endif

The problem is that adding the “s” parameter in query_posts() gives me zero results no matter what the “s” value is. It seems like the whole search mechanism is not working at all.

I’m getting results, only if I remove “s” parameter or set it to ”.

Any suggestions?