Fomantic-UI: Less-loader error

I tried to switch from the semantic-ui-less to fomantic-ui-less and I hoped for it to be seamless. However, I get an error from the less-loader:

ERROR in ./node_modules/fomantic-ui-less/semantic.less (./node_modules/css-loader!./node_modules/less-loader/dist/cjs.js!./node_modules/fomantic-ui-less/semantic.less)
Module build failed (from ./node_modules/less-loader/dist/cjs.js):


  @isDark                     : @colors[@@color][isDark];
  @_labelColor                : @colors[@@color][color];
                                     ^
Unrecognised input
      in /Users/user/Projects/project/node_modules/fomantic-ui-less/definitions/elements/label.less (line 622, column 39)
 @ ./node_modules/fomantic-ui-less/semantic.less 4:14-92 14:3-18:5 15:22-100
 @ ./src/main.js
 @ multi ./build/dev-client ./src/main.js

I tried different versions of the fomantic-ui-less and less-loader. My webpack and loader configuration worked with semantic-ui-less so I believe it should work the same with fomantic-ui-less.