Fails to run npm rebuild?

[YourDeveloperFriend]

I'm not quite sure what is happening, but bcrypt is giving me an error that makes me think that "npm rebuild" is not being run properly. I set the following engine in package.json:

node: 0.10.25
npm: 1.3.21

And to temporarily fix the error, I changed my procfile:
web: npm rebuild && node server.js

And it works. This leads me to believe that somehow npm rebuild is not being properly run.

[YourDeveloperFriend]

Oh, you don't run npm rebuild unless node_modules is checked into the repo. That probably means that bcrypt is not installing correctly. Never mind.