diff --git a/sw/airborne/subsystems/datalink/telemetry.c b/sw/airborne/subsystems/datalink/telemetry.c
index 4dca1d0164..6e4292c823 100644
--- a/sw/airborne/subsystems/datalink/telemetry.c
+++ b/sw/airborne/subsystems/datalink/telemetry.c
@@ -46,8 +46,8 @@ struct periodic_telemetry pprz_telemetry = { TELEMETRY_NB_MSG, telemetry_msgs, t
  */
 int8_t register_periodic_telemetry(struct periodic_telemetry *_pt, const char *_msg, telemetry_cb _cb)
 {
-  // return FALSE if NULL is passed as periodic_telemetry
-  if (_pt == NULL) { return FALSE; }
+  // return if NULL is passed as periodic_telemetry
+  if (_pt == NULL) { return -1; }
   // look for message name
   uint8_t i, j;
   for (i = 0; i < _pt->nb; i++) {
diff --git a/sw/tools/generators/gen_periodic.ml b/sw/tools/generators/gen_periodic.ml
index 205c02292b..fef8b52090 100644
--- a/sw/tools/generators/gen_periodic.ml
+++ b/sw/tools/generators/gen_periodic.ml
@@ -163,12 +163,8 @@ let print_message_table = fun out_h xml ->
   fprintf out_h "};\n\n";
   fprintf out_h "#define TELEMETRY_CBS_NULL { \\\n";
   for i = 1 to (Hashtbl.length messages) do
-    fprintf out_h "  {{";
-    (* TODO: fix hardcoded value of 4 *)
-    for j = 1 to 4 do
-      fprintf out_h "NULL, "
-    done;
-    fprintf out_h "}}, \\\n"
+    (* use one 0 to init all slots (number TELEMETRY_NB_CBS) to NULL *)
+    fprintf out_h "  {{ NULL }}, \\\n";
   done;
   fprintf out_h "}\n\n"