When WP_DEBUG_DISPLAY is set to true just blank page

I have been trying to debug issues on my WordPress install however when I define the following things in my wp-config.php and access the page with the error I want to see the screen is just a blank white page.

This is what I add to my wp-config.php file.

define('WP_DEBUG', true);
define('WP_DEBUG_DISPLAY', true);