AJAX and php protected files

I have a php code within a php file. I have a slender protection of that file, something like:

[code=php]
if(!defined(‘foo’)){header(‘HTTP/1.0 404 not found’);exit;}
[/code]

Now, this php file has a query function (to a MYSQL D?. It works ok, [I]in a static[/I] manner (as an include). But the moment I try an AJAX request, the code above is activated and no response is sent back to the AJAX object.

Any idea how to protect a php file on which I need to send an AJAX request?

Also in #PHP _↴