htaccess - redirigir la dirección del directorio a la página exacta en él

Sorry if I am using wrong terminology, while writing this question. I have a page in the directory on my website:

lorumipsum.com/dir/index.php

I would like to redirect to that page everyone, who would write address

lorumipsum.com/dir

in their browsers. How would would I do that? I tried writing in htaccess this line:

Redirect 301 /dir lorumipsum.com/dir/index.php

pero no parece funcionar.