Debugging Gulpfile with node-inspector takes long to start

I am trying to debug my gulp taks with node-inspector by running it like this

node-debug $(which gulp) build

and that works, except my Gulpfile is not .js but .coffee and for some reason it hangs for almost a minute in the beginning saying:

Requiring external module coffee-script/register

It doesn't take that long when I run it normally and it starts node-inspector almost instantly if I use Gulpfile.js. Why is it taking too long when I use Gulpfile.coffee?

It's not a big deal, yet a bit annoying