--- ntp-4.2.4p7-orig/configure.ac	2009-06-18 14:48:12.151346763 +0200
+++ ntp-4.2.4p7/configure.ac	2009-06-18 14:50:07.054692531 +0200
@@ -4456,6 +4456,7 @@
 		[
 		    AC_LANG_PROGRAM(
 			[
+                            #define _GNU_SOURCE
 			    #include <sys/types.h>
 			    #include <sys/socket.h>
 			    #include <netinet/in.h>