For some reason my blog mod rewrite isn't working.

RewriteRule ^blog/([0-9]+)/(.*)$ /blog.php?post_id=$1&title=$2 [L]

When I visit my blog page and write:

echo $_GET['post_id']; die();

Nothing is returned. In order for a user to go to an individual blog page I need that id returned. Any idea as to what I am missing?