How can I exclude sticky post from custom loop?

I inserted a custom-loop in my template and the custom-loop would display 4 random entries. Everything went smoothly until used a sticky post. The custom-loop which should displayed only 4 entries now displayed 5 entries which messed up the design.

Can anyone tell me how to exclude sticky post from custom loop?

oh… and here’s my custom-loop code:

<div id="random-posts">
<?php
$my_query = new WP_Query('orderby=rand&showposts=4');
while ($my_query->have_posts()) : $my_query->the_post();
?>

  [SOME STUFF]

</div><!-- #random-posts -->

<?php endwhile; ?>
<?php wp_reset_postdata(); ?>