Hiding index of /blog

So i used the tutorial Giving_WordPress_Its_Own_Directory https://codex.www.ads-software.com/Giving_WordPress_Its_Own_Directory

I made the directory at domain.com/blog and made the blog show up at domain.com.

However, the problem is that when i put domain.com/blog into the url it shows all the files in that folder. How do I hide this? Thanks!