sass-rails: file.css(.scss).erb causes `File to import not found or unreadable`

Using the ERB handler breaks reading/importing the files…

This works:

// application.css.scss:
@import 'tester'

// tester.css(.scss)
body { color: #ABC; }

This does not:

// application.css.scss:
@import 'tester'

// tester.css(.scss).erb
body { color: #ABC; }

Sass::SyntaxError: File to import not found or unreadable

At first I thought it was related to #119 or #94, but those fixes don’t solve my problem. I do use Rails 4.0.0.beta1 (together with sass-rails 4.0.0.beta1), so perhaps this could be related?