Defined constants - FCPATH

Hi

I got a problem with defined constant. FCPATH...
...
// Path to the front controller (this file)
define('FCPATH', dirname(__FILE__).'/');
...
exactly the part '/' makes problem to me.
in windows local, this code:

$path = FCPATH . $folder;
echo $path;

is generating something like:

D:\xampp\docs\domain/orders

And it's a problem. Easy way to correct this, is to use DIRECTORY_SEPARATOR instead of '/'.
But it isn't very good practice to edit index.php file.

Please give me an idea, what is the best to do...

Thanks.