I was able to fix using the patch from Debian bug report #785150. It only partially applies to fglrx-core 15.200, but still works.
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=785150 Steps to fix: 1. Download patch from #785150 -- https://bugs.debian.org/cgi-bin/bugreport.cgi?msg=15;filename=fglrx-14.12_fix_build_4.0.0-1-amd64.patch;att=1;bug=785150 2. cd /usr/src/fglrx-core-15.200 3. patch -p1 < ~/Downloads/fglrx...patch 4. sudo dkms install -m fglrx -v 13.251 -k 4.0.4-040004-generic Reboot and enjoy :) ** Bug watch added: Debian Bug tracker #785150 http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=785150 -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1456445 Title: fglrx-core 2:15.200-0ubuntu4: fglrx-core kernel module failed to build [error: implicit declaration of function ‘read_cr4’] To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/fglrx-installer/+bug/1456445/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs