diff -up mtr-0.75/net.c.fd-flags mtr-0.75/net.c

--- mtr-0.75/net.c.fd-flags	2008-10-22 08:07:53.000000000 +0200

+++ mtr-0.75/net.c	2008-10-23 13:57:04.000000000 +0200

@@ -945,8 +945,9 @@ int net_preopen(void) 

   set_fd_flags(recvsock4);

 #ifdef ENABLE_IPV6

   recvsock6 = socket(AF_INET6, SOCK_RAW, IPPROTO_ICMPV6);

+  if (recvsock6 >= 0)

+    set_fd_flags(recvsock6);  

 #endif

-  set_fd_flags(recvsock6);

   return 0;

 }