Index: ext/socket/extconf.rb
===================================================================
--- ext/socket/extconf.rb	(revision 41241)
+++ ext/socket/extconf.rb	(working copy)
@@ -294,6 +294,10 @@ end
 
 $INCFLAGS << " -I$(topdir) -I$(top_srcdir)"
 
+if /darwin/ =~ RUBY_PLATFORM
+  $CFLAGS << " -D__APPLE_USE_RFC_3542"
+end
+
 headers = []
 unless $mswin or $mingw
   headers = %w<sys/types.h netdb.h string.h sys/socket.h netinet/in.h>