mod_rewrite从单个页面中删除.php文件扩展名的问题

So I've been trying to remove the extension from a single page on a site of mine.

My code in httpd.conf looks like this:

RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^refer$ refer.php [L]

However, when I go to /refer, it says a 404 and that "The requested URL /refer was not found on this server."

How can I rewrite only a single file in this way?

Thanks!