As [reported to MacPorts](https://trac.macports.org/ticket/73183) by @barracuda156, htpdate 2.0.1 fails to build on Mac OS X 10.5: ``` htpdate.c:48:10: fatal error: sys/timex.h: No such file or directory 48 | #include <sys/timex.h> | ^~~~~~~~~~~~~ ``` The sys/timex.h header first appeared in macOS 10.13.