The entry 'OS X' classifies Chrome OS as OS X by matching the sub-string Cr"OS x"86. Example user-agent: Mozilla/5.0 (X11; CrOS x86_64 7520.62.0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/47.0.2526.80 Safari/537.36 Putting CrOS higher up the list fixed it.