diff --git a/sw/ground_segment/tmtc/server.ml b/sw/ground_segment/tmtc/server.ml
index 6203cdfa9f..374a191c43 100644
--- a/sw/ground_segment/tmtc/server.ml
+++ b/sw/ground_segment/tmtc/server.ml
@@ -26,6 +26,7 @@
 
 let my_id = "ground"
 let gps_mode_3D = 3
+let no_md5_check = ref false
 
 open Printf
 open Latlong
@@ -36,6 +37,7 @@ module LL = Latlong
 
 module Ground = struct let name = "ground" end
 module Ground_Pprz = Pprz.Messages(Ground)
+module Tm_Pprz = Pprz.Messages (struct let name = "telemetry" end)
 module Alerts_Pprz = Pprz.Messages(struct let name = "alert" end)
 module Dl_Pprz = Pprz.Messages (struct let name = "datalink" end)
 
@@ -413,16 +415,44 @@ let get_conf = fun real_id id conf_xml ->
       Hashtbl.add unknown_aircrafts real_id ();
       failwith (sprintf "Error: A/C '%s' not found" id)
 
+let check_md5sum = fun ac_name alive_md5sum aircraft_conf_dir ->
+  (* Read the digest generated by sw/tools/gen_aircraft *)
+  let f = open_in (aircraft_conf_dir // "aircraft.md5") in
+  let md5sum = input_line f in
+  close_in f;
+
+  try
+    match alive_md5sum with
+      Pprz.Array array ->
+	let n = Array.length array in
+	assert(n = String.length md5sum / 2);
+	for i = 0 to n - 1 do
+	  let x = int_of_string (sprintf "0x%c%c" md5sum.[2*i] md5sum.[2*i+1]) in
+	  assert (x = Pprz.int_of_value array.(i))
+	done
+    | _ -> failwith "Array expected here"
+  with _ ->
+    let error_message = sprintf "WARNING: live md5 signature for %s does not match current configuration, please reload your code (disable check with -no_md5_check option)" ac_name in
+    if !no_md5_check then
+      fprintf stderr "%s; continuing anyway as requested\n%!" error_message
+    else
+      failwith  error_message
+
       
-let new_aircraft = fun real_id ->
+let new_aircraft = fun alive_md5sum real_id ->
   let id, root_dir, conf_xml = replayed real_id in
   let conf = get_conf real_id id conf_xml in
   let ac_name = ExtXml.attrib conf "name" in
-  let fp_file = Env.paparazzi_home // root_dir // "var" // ac_name // "flight_plan.xml" in
+  let var_aircraft_dir = Env.paparazzi_home // root_dir // "var" // ac_name in
+
+  let fp_file =  var_aircraft_dir // "flight_plan.xml" in
   let xml_fp = ExtXml.child (Xml.parse_file fp_file) "flight_plan" in
 
-  let airframe_file = Env.paparazzi_home // root_dir // "conf" // ExtXml.attrib conf "airframe" in
+  let aircraft_conf_dir = var_aircraft_dir // "conf" in
+  let airframe_file =  aircraft_conf_dir // ExtXml.attrib conf "airframe" in
   let airframe_xml = Xml.parse_file airframe_file in
+
+  check_md5sum real_id alive_md5sum aircraft_conf_dir;
   
   let ac = Aircraft.new_aircraft real_id ac_name xml_fp airframe_xml in
   let update = fun () ->
@@ -507,11 +537,12 @@ let register_aircraft = fun name a ->
 
 
 (** Identifying message from an A/C *)
-let ident_msg = fun log name ->
+let ident_msg = fun log name vs ->
   try
     if not (Hashtbl.mem aircrafts name) && 
       not (Hashtbl.mem unknown_aircrafts name) then
-      let ac, messages_xml = new_aircraft name in
+      let md5sum = Pprz.assoc "md5sum" vs in
+      let ac, messages_xml = new_aircraft md5sum name in
       let ac_msg_closure = ac_msg messages_xml log name ac in
       let _b = Ivy.bind (fun _ args -> ac_msg_closure args.(0)) (sprintf "^%s +(.*)" name) in
       register_aircraft name ac;
@@ -525,8 +556,7 @@ let new_color = fun () ->
 (* Waits for new aircrafts *)
 let listen_acs = fun log ->
   (** Wait for any message (they all are identified with the A/C) *)
-  ignore (Ivy.bind (fun _ args -> ident_msg log args.(0)) "^(.*) ALIVE");
-  ignore (Ivy.bind (fun _ args -> ident_msg log args.(0)) "^(.*) PPRZ_MODE")
+  ignore (Tm_Pprz.message_bind "ALIVE" (ident_msg log))
 
 
 let send_config = fun http _asker args ->
@@ -559,7 +589,7 @@ let send_config = fun http _asker args ->
       "ac_name", Pprz.String ac_name ]
   with
     Not_found ->
-      failwith (sprintf "ground UNKNOWN %s" ac_id')     
+      failwith (sprintf "ground UNKNOWN %s" ac_id')
     
 let ivy_server = fun http ->
   ignore (Ground_Pprz.message_answerer my_id "AIRCRAFTS" send_aircrafts_msg);
@@ -629,11 +659,12 @@ let _ =
 
   let options =
     [ "-b", Arg.String (fun x -> ivy_bus := x), (sprintf "Bus\tDefault is %s" !ivy_bus);
-      "-n", Arg.Clear logging, "Disable log";
+      "-hostname", Arg.Set_string hostname, "<hostname> Set the address for the http server";
+      "-http", Arg.Set http, "Send http: URLs (default is file:)";
       "-kml", Arg.Set Kml.enabled, "Enable KML file updating";
       "-kml_port", Arg.Set_int Kml.port, (sprintf "Port for KML files (default is %d)" !Kml.port);
-      "-hostname", Arg.Set_string hostname, "<hostname> Set the address for the http server";
-      "-http", Arg.Set http, "Send http: URLs (default is file:)"] in
+      "-n", Arg.Clear logging, "Disable log";
+      "-no_md5_check", Arg.Set no_md5_check, "Disable safety matching of live and current configurations"] in
   Arg.parse (options)
     (fun x -> Printf.fprintf stderr "%s: Warning: Don't do anything with '%s' argument\n" Sys.argv.(0) x)
     "Usage: ";
diff --git a/sw/tools/gen_aircraft.ml b/sw/tools/gen_aircraft.ml
index 337aaab74d..2c0e011c87 100644
--- a/sw/tools/gen_aircraft.ml
+++ b/sw/tools/gen_aircraft.ml
@@ -92,6 +92,10 @@ let _ =
   close_out f;
 
   let md5sum = Digest.to_hex (Digest.file conf_aircraft_file) in
+  let md5sum_file = aircraft_conf_dir // "aircraft.md5" in
+  let f = open_out md5sum_file in
+  Printf.fprintf f "%s\n" md5sum;
+  close_out f;
   
   let c = sprintf "make -f Makefile.ac AIRCRAFT=%s AC_ID=%s AIRFRAME_XML=%s RADIO=%s FLIGHT_PLAN=%s TELEMETRY=%s SETTINGS=\"%s\" MD5SUM=\"%s\" all_ac_h" aircraft (value "ac_id") (value "airframe") (value "radio") (value "flight_plan") (value "telemetry") settings md5sum in
   begin (** Quiet is speficied in the Makefile *)