FORCE SSL ADMIN has a redirect loop

Hi,

I’m going to use HTTPS only on my blog, just follow the codex guide to force to use SSL for Wp-admin. But the result is a redirect loop when I’m trying to load /wp-admin

My config:

# Force SSL login
define( 'FORCE_SSL_ADMIN', true );
define( 'FORCE_SSL_LOGIN', true );
if ($_SERVER['HTTP_X_FORWARDED_PROTO'] == 'https')
        $_SERVER['HTTPS']='on';

Redirect loops: http://i.imgur.com/tsjMGOw.png