diff --git a/src/vnet/tcp/tcp_output.c b/src/vnet/tcp/tcp_output.c
index 5172fca..61692fa 100644
--- a/src/vnet/tcp/tcp_output.c
+++ b/src/vnet/tcp/tcp_output.c
@@ -667,6 +667,7 @@
 
   b = vlib_get_buffer (vm, bi);
   tcp_init_buffer (vm, b);
+  vnet_buffer (b)->tcp.connection_index = tc->c_c_index;
 
   /* Make and write options */
   tcp_hdr_len = sizeof (tcp_header_t);