This fixes an upstream bug:

    https://github.com/traviscross/mtr/issues/35

The patch is from

    https://bugs.launchpad.net/mtr/+bug/1273486/comments/5

--- mtr-0.86/net.c	2014-12-09 03:20:57.000000000 -0800
+++ mtr-0.86/net.c	2015-03-20 09:43:55.576572132 -0700
@@ -301,7 +301,7 @@ void net_send_tcp(int index)
 void net_send_tcp(int index)
 {
   int ttl, s;
-  int opt = 1;
+  int flags;
   int port;
   struct sockaddr_storage local;
   struct sockaddr_storage remote;
@@ -354,10 +354,10 @@ void net_send_tcp(int index)
     exit(EXIT_FAILURE);
   }
 
-  opt = 1;
-  if (ioctl(s, FIONBIO, &opt)) {
+  flags = fcntl(s, F_GETFL, 0);
+  if (fcntl(s, F_SETFL, flags | O_NONBLOCK) == -1) {
     display_clear();
-    perror("ioctl FIONBIO");
+    perror("fcntl F_SETFL(O_NONBLOCK)");
     exit(EXIT_FAILURE);
   }