I wasn't sure who to send this message to so I hope posting to the list is ok (I'm not a subscriber). This isn't a bug but more a message to the maintainers that there is newer of version of autoconf that recognises MacOSX. I was able to download the latest version and do the following: cd /usr/local/src/rsync-2.4.6 cp /usr/local/src/autoconf-2.52/config/config.sub . ./configure --host=ppc-apple-macosx It compiled cleanly, linked with some warnings (MacOSX specific), and worked just fine.