StealJS build error - 'MODULE_NOT_FOUND' } Error: Cannot find module 'less'

Loading my application with StealJS in development works great. When I try to build a production version. I'm getting a 'MODULE_NOT_FOUND' } Error: Cannot find module 'less'. If I remove the 'style.less!' file dependency the build works.

The docs say, "CSS and Less plugins come by default". So I don't have less defined in my stealconfig ext object. Do I need to load less?

patricks-MacBook-Pro:www patrickclancy$ grunt build
Running "stealBuild:default" (stealBuild) task
error { [Error: Cannot find module 'less'] code: 'MODULE_NOT_FOUND' } Error: Cannot find module 'less'
    at Function.Module._resolveFilename (module.js:338:15)
    at Function.Module._load (module.js:280:25)
    at Module.require (module.js:364:17)
    at require (module.js:380:17)