diff --git a/ChangeLog b/ChangeLog
index 9d90f51..4de8e87 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -2,6 +2,10 @@
 
 	* configure.ac: Add back check for inet_aton, which got dropped
 	  somehow in previous jumbo patch.
+	  Use AC_GNU_SOURCE to define _GNU_SOURCE, rather than having
+	  lib/zebra.h do it.
+	  AC_FUNC_STRNLEN has side-effects with latest autoconf, use 
+	  AC_CHECK_FUNC on strnlen instead.
 
 2007-05-09 Paul Jakma <paul.jakma@sun.com>
 
diff --git a/configure.ac b/configure.ac
index f4966d8..fe127a4 100755
--- a/configure.ac
+++ b/configure.ac
@@ -163,10 +163,11 @@
 	]
 )
 
-dnl ---------
-dnl AIX check
-dnl ---------
+dnl -----------------
+dnl System extensions
+dnl -----------------
 AC_AIX
+AC_GNU_SOURCE
 
 dnl -------
 dnl libtool
@@ -640,7 +641,10 @@
 AC_FUNC_STAT
 AC_FUNC_SELECT_ARGTYPES
 AC_FUNC_STRFTIME
-AC_FUNC_STRNLEN
+dnl Avoid AC_FUNC_STRNLEN because it pulls in AC_SYSTEM_EXTENSIONS which
+dnl can lead to strange side effects.  So we just check for strnlen
+dnl directly, see below.
+dnlAC_FUNC_STRNLENdnl
 AC_FUNC_VPRINTF
 
 dnl -------------------------------
@@ -665,7 +669,7 @@
 dnl other functions
 dnl ---------------
 AC_CHECK_FUNCS([dup2 ftruncate getcwd gethostbyname getpagesize gettimeofday \
-	inet_ntoa inet_aton \
+	inet_ntoa inet_aton strnlen \
 	memchr memmove memset select socket \
 	strcasecmp strchr strcspn strdup strerror \
 	strncasecmp strndup strrchr strspn strstr \
diff --git a/lib/ChangeLog b/lib/ChangeLog
index 5666cba..4360c83 100644
--- a/lib/ChangeLog
+++ b/lib/ChangeLog
@@ -1,3 +1,7 @@
+2007-05-10 Paul Jakma <paul.jakma@sun.com>
+
+	* zebra.h: Don't try define _GNU_SOURCE, autoconf should do it.
+
 2007-05-03 Paul Jakma <paul.jakma@sun.com>
 
 	* memtypes.c: Add MTYPE_ATTR_EXTRA and MTYPE_BGP_ROUTE_EXTRA
diff --git a/lib/zebra.h b/lib/zebra.h
index 3c01aec..2451dbe 100644
--- a/lib/zebra.h
+++ b/lib/zebra.h
@@ -25,10 +25,6 @@
 #include "config.h"
 #endif /* HAVE_CONFIG_H */
 
-#ifdef GNU_LINUX
-#define _GNU_SOURCE
-#endif /* GNU_LINUX */
-
 #ifdef SUNOS_5
 #define _XPG4_2
 #define __EXTENSIONS__