Ember addon ember-cli-sass issue

I have used .css in my Ember addon, now I want to use SCSS. First I changed extensions of style files to .scss, I have app.scss in addon/styles that includes other style files for components etc.

I also added ember-cli-sass (6.0.0) version as dependecy in package.json. Now when I try to serve ember addon, I get following error:

File not found: /addon.scss
in any of the following include paths:
  .../ember/addons/my-addon/tmp/sass_compiler-input_base_path-b2aPW625.tmp
Error: File not found: /addon.scss
in any of the following include paths:
  .../ember/addons/my-addon/tmp/sass_compiler-input_base_path-b2aPW625.tmp
    at Object.findFileSync (.../ember/addons/v/node_modules/include-path-searcher/index.js:12:9)
    at SassCompiler.build (.../ember/addons/v/node_modules/graph-lib/node_modules/broccoli-sass-source-maps/index.js:63:31)
    at .../ember/addons/v/node_modules/broccoli-caching-writer/index.js:149:21
    at tryCatch (.../ember/addons/my-addon/node_modules/rsvp/dist/rsvp.js:538:12)
    at invokeCallback (.../ember/addons/my-addon/node_modules/rsvp/dist/rsvp.js:553:13)
    at publish (.../ember/addons/my-addon/node_modules/rsvp/dist/rsvp.js:521:7)
    at flush (.../ember/addons/my-addon/node_modules/rsvp/dist/rsvp.js:2373:5)
    at _combinedTickCallback (internal/process/next_tick.js:67:7)
    at process._tickCallback (internal/process/next_tick.js:98:9)

Any idea what is causing this issue? Do I need to add/edit anything else in my addon? I am using ember-cli 2.3.0. I have tried adding addon.scss file, it didnt help.