Problem with adding filter

Hey Guys and Gals.

I just wrote a little piece of code that adds nofollow tags to my WP posts. Here is the code:


<?php
function addnofollow($text) {
return str_replace('<a href=', '<a rel="nofollow" href=', $text);
}
add_filter('the_content', 'addnofollow');
?>


Now it all works very well except when I try to view my RSS feed. I get the following error:

Warning: Cannot modify header information – headers already sent by (output started at /home/cfml/public_html/wp-content/plugins/addnofollow.php:12) in /home/cfml/public_html/wp-includes/feed-rss2.php on line 2

Any ideas what is causing this?