Thanks @sevikerr, I'm merging.

Thanks a lot! 🔥

Thank you for your contribution, it resolves my problem.
Is there a new release contains the changing? @jakubpawlowicz

I'll do my best to push one this week.

@woody-li The fix is out in 5.3.2.

Got it, thanks.

For those who searching solution for Gulp project with gulp-clean-css plugin, you need to override clean-css version in packedge.json
{
"name": "...",
...
"scripts": {
....
},
"devDependencies": {
"gulp": "^4.0.2",
"gulp-clean-css": "^4.3.0",
...
"clean-css": "^5.3.3"
},
"overrides": {
....
"clean-css": "$clean-css"
}
}