Sourcemaps displays mixins instead of pages in the inspector. How to fix?

Question

gulp.js

Wrote mixins for media queries. And now everything that is written in these mixins refers in the inspector to the place where the mixin is declared, and not to the place where the rules were described.
I'll give you an example. There is a variables.styl file that describes the mixin. And there is a header.styl file, in which some of the styles are described in the media query (i.e. through this mixin). I open the inspector in the browser and see that the code maps refer to the variables file, not the header.
There is no such problem in SCSS. But he refused SCSS due to slowness.