+dnl POSIXCHECK is worthwhile for maintainers, but adds several seconds
+dnl (more than 10% execution time) to ./configure, with no benefit for
+dnl most users. Using it to look for bugs requires:
+dnl GNULIB_POSIXCHECK=1 autoreconf -f
+dnl ./configure
+dnl make
+dnl make -C src clean
+dnl make CFLAGS=-DGNULIB_POSIXCHECK=1
+dnl FIXME: Once we figure out how to avoid false positives, we should
+dnl have 'make my-distcheck' in dist-check.mk exercise this.
+m4_syscmd([test "${GNULIB_POSIXCHECK+set}" = set])
+m4_if(m4_sysval, [0], [], [dnl
+gl_ASSERT_NO_GNULIB_POSIXCHECK])
+