diff -r -u bug.orig/spawn.ml bug/spawn.ml
--- bug.orig/spawn.ml	2015-02-04 16:28:38.000000000 +0100
+++ bug/spawn.ml	2015-05-14 02:35:27.026125000 +0200
@@ -61,12 +61,13 @@
   let r, _, _ = Unix.select [s] [] [] accept_timeout in
   if r = [] then raise (Failure (Printf.sprintf
     "The spawned process did not connect back in %2.1fs" accept_timeout));
-  let cs, _ = Unix.accept s in
+  let csi, _ = Unix.accept s in
+  let cso, _ = Unix.accept s in
   Unix.close s;
-  let cin, cout = Unix.in_channel_of_descr cs, Unix.out_channel_of_descr cs in
+  let cin, cout = Unix.in_channel_of_descr csi, Unix.out_channel_of_descr cso in
   set_binary_mode_in cin true;
   set_binary_mode_out cout true;
-  cs, cin, cout
+  csi, cin, cout

 let handshake cin cout =
   try
diff -r -u bug.orig/spawned.ml bug/spawned.ml
--- bug.orig/spawned.ml	2015-02-04 16:31:52.000000000 +0100
+++ bug/spawned.ml	2015-05-14 02:36:39.307375000 +0200
@@ -30,7 +30,8 @@

 let open_bin_connection h p =
   let open Unix in
-  let cin, cout = open_connection (ADDR_INET (inet_addr_of_string h,p)) in
+  let _, cout = open_connection (ADDR_INET (inet_addr_of_string h,p)) in
+  let cin, _ = open_connection (ADDR_INET (inet_addr_of_string h,p)) in
   set_binary_mode_in cin true;
   set_binary_mode_out cout true;
   cin, cout