diff --git a/configure.ac b/configure.ac
index 5a865f8e1..2eede34c3 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1348,6 +1348,13 @@ EOD
 	AC_DEFINE([BROKEN_SETVBUF], [1],
 	    [LynxOS has broken setvbuf() implementation])
 	;;
+*-*-gnu*)
+	dnl GNU Hurd.  Needs to be after the linux and the other *-gnu entries.
+	dnl Target SUSv3/POSIX.1-2001 plus BSD specifics.
+	dnl _DEFAULT_SOURCE is the new name for _BSD_SOURCE
+	dnl _GNU_SOURCE is needed for setres*id prototypes.
+	CPPFLAGS="$CPPFLAGS -D_XOPEN_SOURCE=600 -D_BSD_SOURCE -D_DEFAULT_SOURCE -D_GNU_SOURCE"
+	;;
 esac
 
 AC_MSG_CHECKING([compiler and flags for sanity])