Missing space in minified CSS

I have the following CSS in my style.css:

@supports((-webkit-animation-fill-mode: forwards) or (animation-fill-mode: forwards)) {
...
}

which in turn gets minified to

@supports((-webkit-animation-fill-mode:forwards) or(animation-fill-mode:forwards)) {...}

Note the missing space after or. This missing space makes browsers ignore the rule, unfortunately. Is this a bug within the minifier or can I adjust my CSS to survive the minification. Or is there even a possibility to combine CSS, but not minify it?

– Thomas