Ember.js: Cannot read property 'isHelperInstance' of undefined

I'm deploying my app to my staging environment for the first time, but I'm running into an error...One of my routes is unable to render its template. I'm seeing this error in the console:

Uncaught TypeError: Cannot read property 'isHelperInstance' of undefined

I was not seeing this error in development.

I'm using ember-cli-rails to serve the app using Heroku.

How can I solve this issue?