I installed Mac OSX 10.9 the day it came out. Afterwards I decided I needed to install PIL. I'd installed it before, but it appeared the update had broken that. When I try to use pip to install PIL, it fails when building _imaging. It appears the root cause is this. /usr/include/sys/cdefs.h:655:2: error: Unsupported architecture Theres also a similar error here: /usr/include/machine/limits.h:8:2: error: architecture not supported and here: /usr/include/machine/_types.h:34:2: error: architecture not supported Then there's a whole list of missing types. /usr/include/sys/_types.h:94:9: error: unknown type name '__int64_t' typedef __int64_t __darwin_blkcnt_t; /* total blocks */ ^ /usr/include/sys/_types.h:95:9: error: unknown type name '__int32_t' typedef __int32_t __darwin_blksize_t; /* preferred block size */ ^ /usr/include/sys/_types.h:96:9: error: unknown type name '__int32_t' typedef __int32_t __darwin_dev_t; /* dev_t */ ^ /usr/include/sys/_types.h:99:9: error: unknown type name '__uint32_t' typedef __uint32_t __darwin_gid_t; /* [???] process and group IDs */ ^ /usr/include/sys/_types.h:100:9: error: unknown type name '__uint32_t' typedef __uint32_t __darwin_id_t; /* [XSI] pid_t, uid_t, or gid_t*/ ^ /usr/include/sys/_types.h:101:9: error: unknown type name '__uint64_t' typedef __uint64_t __darwin_ino64_t; /* [???] Used for 64 bit inodes */ Needless to say I don't know where to go from here. I've got a couple of guesses, but I don't even know how to check. Wrong include probably as a result of a badly configured environment variable Problem with Xcode's installation/ missing command line tools Messed up header files If anyone has any suggestions either to check one of those possibilities or for one of their own I'm all ears.