I have the following in .htaccess:

RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule (.*) /$1.html [L]
This turns URIs such as domain.com/something into a request for domain.com/something.html, which is what I want. However, if someone types domain.com/something/, I get a 500. I tried the following:

RewriteRule (.*)/?$ /$1.html [L]
But the error persists. Anyone have any ideas of a method for fixing this?