How can I get css sourcemaps to work in this Ember app?

Sass compilation is working fine, but I want to be able to see the source of the style in Chrome developer tool. I have ember-cli-sass installed and in ember-cli-build.js I am sending the following option to the EmberApp constructor.

sassOptions: {
  sourceMap: true
}

Still I see the bundled css file as the source for all styles. Am I missing some other configuration?