$ uname -a
Linux ZdejPoham 4.13.0-32-generic #35-Ubuntu SMP Thu Jan 25 09:13:46 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux

$ nodejs -v
v9.5.0

$ cleancss -v
4.1.10

$ sudo npm install -g clean-css

• clean-css@4.1.9
  updated 1 package in 0.507s

$ cleancss -O2 --inline --compatibility 'ie7' -o frontpage.min.css frontpage.css
/usr/lib/node_modules/clean-css-cli/node_modules/clean-css/lib/options/inline.js:12
rules.split(',');
^

TypeError: rules.split is not a function
at inlineOptionsFrom (/usr/lib/node_modules/clean-css-cli/node_modules/clean-css/lib/options/inline.js:12:11)
at new CleanCSS (/usr/lib/node_modules/clean-css-cli/node_modules/clean-css/lib/clean.js:37:13)
at minify (/usr/lib/node_modules/clean-css-cli/index.js:215:18)
at cli (/usr/lib/node_modules/clean-css-cli/index.js:166:5)
at Object. (/usr/lib/node_modules/clean-css-cli/bin/cleancss:4:8)
at Module._compile (module.js:660:30)
at Object.Module._extensions..js (module.js:671:10)
at Module.load (module.js:573:32)
at tryModuleLoad (module.js:513:12)
at Function.Module._load (module.js:505:3)