FreeBSD doesn't support the int daylight or long timezone in time.h itself. tzcode supports them on OSes which already support them, like OpenBSD. I'm trying to figure out if it should be possible to compile tzcode to support daylight and timezone even on OSes which don't support them. I've saved the output of make (both stdout and stderr) when CFLAGS is set to -DUSG_COMPAT=1 alone into usgcompat.txt I've saved the output of make (both stdout and stderr) when CFLAGS is set to '-DUSG_COMPAT=1 -DHAVE_POSIX_DECLS=0' into both.txt What I'm seeing is that the OS's time.h is being included, under both configurations. This topic originated in this thread: http://mm.icann.org/pipermail/tz/2019-November/028596.html http://mm.icann.org/pipermail/tz/2019-November/thread.html