This seems to be a bug, because "linode.com" is not on the public suffix list. Several subdomains and related domains are, but not linode.com: // Linode : https://linode.com // Submitted by <security@linode.com> members.linode.com *.nodebalancer.linode.com *.linodeobjects.com ip.linodeusercontent.com I would expect get_public_suffix("ns1.linode.com") to return "linode.com"