It's unlikely that future versions will require _POSIX_C_SOURCE
diff --git a/configure b/configure
index ccdf62e..8da9b5e 100755
--- a/configure
+++ b/configure
@@ -1588,7 +1588,7 @@
   # disables platform specific features beyond repair.
   # On Mac OS X 10.3, defining _POSIX_C_SOURCE or _XOPEN_SOURCE
   # has no effect, don't bother defining them
-  Darwin/[78].*)
+  Darwin/[789].*)
     define_xopen_source=no
     ;;