--- src/lib/libast/features/standards.orig	2017-11-30 22:35:04 UTC
+++ src/lib/libast/features/standards
@@ -1,5 +1,19 @@
 set stdio
-if tst note{ _GNU_SOURCE works }end compile{
+# In FreeBSD, definitions like _POSIX_SOURCE and such are used to *limit*
+# functionality to known API; they don't enable anything. The general intent in
+# BSD is to enable everything by default (effectively, providing the
+# _KITCHEN_SINK_SOURCE mentioned below). So we look for that here, but stay
+# careful that we don't get fooled by presence of FreeBSD that underpins some
+# subsystems in Mac OS X; there are other Apple-specific portability hacks
+# elsewhere we should not interfere with.
+if tst note{ FreeBSD }end compile{
+		#include <sys/param.h>
+		#if !defined(__FreeBSD__) || defined(APPLE)
+		#error not a FreeBSD system
+		#endif
+	}end {
+	}
+elif tst note{ _GNU_SOURCE works }end compile{
 		#define _GNU_SOURCE 1
 		#include <sys/types.h>
 		#include <sys/stat.h>