This should be a straight forward problem but it is driving me mad trying to get it to work!

What im trying to do:
I have a file - index.html which contains php code but i want it to appear to be a html file. Straight forward enough.

There for in .htaccess i have put in the following code
AddType application/x-httpd-php .html

which should map the html file on the php application, right?

However all i get is a 500 internal server error.

The file in question runs fine with a .php extension.

Help!