diff --git a/configure.ac b/configure.ac
index f70a4a7..8cede20 100644
--- a/configure.ac
+++ b/configure.ac
@@ -4,7 +4,8 @@ dnl Minimum Autoconf version required.
 AC_PREREQ(2.59)
 
 AC_INIT([fping],[5.1])
-AC_GNU_SOURCE
+
+m4_ifdef([AC_AUTOCONF_VERSION],[AC_USE_SYSTEM_EXTENSIONS], [AC_GNU_SOURCE])
 
 dnl --disable-ipv4
 AC_ARG_ENABLE([ipv4],