CSS lint and SASS @extend

Currently I'm working on a UI kit that needs to be highly reusable, modular, and, well, basically plug-and-play to a Drupal build later on.

I'm also a fan of CSSLint and am finding myself at a cross-roads.

Using SASS, I like the idea of @extend'ing styles. So we'll have, for example, a heading;

h1 {  
    @extend .fw600; // font weight 600
    @extend .text-white; // color: white;
    font-size: $font-medium;

    @media( min-width: $screen-sm ) {
       font-size: $font-large;
    }
}

Now running the compiled CSS through a linter, we get warnings about headings should only be defined once.

I'm unsure on how to do this in a way that that will appease the lint Gods. Perhaps, as I'm using SASS, I should use a SASS linter instead?