.htaccess for wordpress in separate folder

I’m working on a really odd site which has a couple of Magento installs next to a WordPress install.

the folder structure looks like this:

/shop (magento)
/shop-world (magento)
/wp
.htaccess

I just installed Yoast on the WordPress install and the first thing it did was edit the WordPress .htaccess settings without creating a backup.

How can I edit this:

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress

So that instead of routing all requests through index.php (which doesn’t exist) the site routes all requests through wp/index.php? I tried adding wp/ on the necessary lines but its not working, and I’m getting an internal server error.

Disclaimer: I didn’t make the site like this – but I do need to fix it without moving all the files.

Rather than change .htaccess, move the index.php up to root, open it, and change:

require( dirname( __FILE__ ) . '/wp-blog-header.php' );

to:

require( dirname( __FILE__ ) . '/wp/wp-blog-header.php' );

In Settings, your WordPress address should be http://example.com/wp, and Site address should be http://example.com.

This process is outlined in the Codex page Giving WordPress Its Own Directory.