Installing Domain Mapping Probs

Morning all...

Was about to set-up Domain Mapping and went through the instructions first.

It states to:
Edit wp-config.php (normally located in the root of your install) and uncomment (remove the //) before the following: //define( 'SUNRISE', 'on' );

But in my wp-config.php file, I do not have the line
//define( 'SUNRISE', 'on' );

This is a very recent fresh WP3.1 install.

What should I do to enable Domain Mapping?