getopt.h:195: error: redefinition of 'struct option'

While working with Gnulib recently I kept running into problems with its getopt-gnu module:

In file included from ../../esio/gnulib/argp.h:24:0,
                 from ../../esio/apps/esio_bench.c:7:
../gnulib/getopt.h:195:8: error: redefinition of ‘struct option’
/usr/include/getopt.h:106:8: note: originally defined here
../gnulib/getopt.h:242:12: error: conflicting types for ‘getopt_long’
/usr/include/getopt.h:175:12: note: previous declaration of ‘getopt_long’ was here
../gnulib/getopt.h:246:12: error: conflicting types for ‘getopt_long_only’
/usr/include/getopt.h:179:12: note: previous declaration of ‘getopt_long_only’ was here
make[2]: *** [esio_bench.o] Error 1

which looked suspiciously like someone else's problem but couldn't be resolved by a simple make distclean.

Turns out that I failed to include the required

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

at the top of my source file. Oops. This detail is obvious in hindsight but slightly difficult to dig out of the relevant section of the gnulib manual.