Enable grid layouts

I am unable to enable grid handling with the autoprefixer. According to https://github.com/postcss/autoprefixer#does-autoprefixer-polyfill-grid-layout-for-ie one has to pass the grid: true option or place a /* autoprefixer grid: on */ comment. But I have no idea where to set this option and the comment seems to be ignored, no matter if I set it at the top of the less-file or before the grid rules.

Input:

/* autoprefixer grid: on */
div {
  /* autoprefixer grid: on */
  display: grid;
}

Command line call:

lessc --autoprefix test.less test.css

Expected output:

div {
  display: -ms-grid;
  display: grid;
}

Actual output:

/* autoprefixer grid: on */
div {
  /* autoprefixer grid: on */
  display: grid;
}

Reproduce the reported lessc --autoprefix test.less test.css case using the shown input, then inspect how the plugin handles the Autoprefixer grid option and comments. Done means the grid setting is honored and the generated CSS contains display: -ms-grid followed by display: grid.