Ember.js: Define a custom RESTAdapter and RESTSerializer?

In the file /app/adapters/application.js, I have the following code:

import Ember from 'ember';
import DS from 'ember-data';

export default DS.RESTAdapter.extend({
  url: 'http://localhose:3000',
  namespace: 'api'
});

export default DS.RESTSerializer.extend({
  keyForAttribute: function(attr, method) {
    return Ember.String.decamelize(attr).toLowerCase();
  },
  primaryKey: '_id'
});

However this results in the following error:

Duplicate default exports.

How should I restructure my code so that they both work?