Ember error: No model was found

When I visit a route that has a model hook:

export default Ember.Route.extend({
  model: function () {
    return this.store.find("account_type");
  }
});

I get this error:

Error while processing route: register No model was found for 'account_type' Error: No model was found for 'account_type'

I have a file in models called account_type.js :

import DS from 'ember-data';

export default  DS.Model.extend({
  type: DS.attr('string')
});

Any ideas?