calc giving wrong result

[aubrijesh]

I am stuck with a small problem. I am trying to use calc function in stylus but it not working. I it giving wrong output always.
I am using grunt-contrib-stylus in grunt task runner.
when I am writting width: calc(100% - 100px); is being generated as width: calc(-300%);.
I tried width: 'calc(100% - 100px)';, width: 'calc(100% - 100px)';, width: calc(100% - 100px); but not worked.
Also tried:calc(unquote('50% - 390px')) calc(50% - 390px)solution given on : https://github.com/stylus/stylus/issues/687 it gives calc(0) as output.My package.json contains "grunt-contrib-stylus": "~0.9.0"