It seems that the extra checks added to Jamtop in 1.3.7 broke the native 64-bit build on Fedora 16: $ jam -f Jambase Argyll Jamrules has been read DESTDIR = '.', PREFIX = '', REFSUBDIR = 'ref' Unable to locate the 32 bit X11 library files Exit 1 $ uname -a Linux pilot 3.3.0-4.fc16.x86_64 #1 SMP Tue Mar 20 18:05:40 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux $ echo $HOSTTYPE x86_64-linux $ echo $MACHTYPE x86_64 $ I don't know much about Jam but I think this is because Jambase expects HOSTTYPE to be x86_64 but there is actually an environment variable with the same name with value x86_64-linux, at least on Fedora 16. It seems to build fine if I copy Jamtop from 1.3.6. Thanks, Bolek