+diff -Ndur linux-2.6.32-orig/net/ipv4/tcp_input.c linux-2.6.32-undorttzero/net/ipv4/tcp_input.c
+--- linux-2.6.32-orig/net/ipv4/tcp_input.c 2013-06-05 15:47:10.551009408 -0400
++++ linux-2.6.32-undorttzero/net/ipv4/tcp_input.c 2013-06-05 15:49:32.458996663 -0400
+@@ -5783,9 +5783,11 @@
+
+ /* tcp_ack considers this ACK as duplicate
+ * and does not calculate rtt.
+- * Force it here.
++ * Fix it at least with timestamps.
+ */
+- tcp_ack_update_rtt(sk, 0, 0);
++ if (tp->rx_opt.saw_tstamp &&
++ tp->rx_opt.rcv_tsecr && !tp->srtt)
++ tcp_ack_saw_tstamp(sk, 0);
+
+ if (tp->rx_opt.tstamp_ok)
+ tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;