diff --git a/include/nigiri/timetable.h b/include/nigiri/timetable.h
index 2a276170..e2ad11a3 100644
--- a/include/nigiri/timetable.h
+++ b/include/nigiri/timetable.h
@@ -23,6 +23,8 @@
 
 namespace nigiri {
 
+constexpr auto const kBinaryVersion = 1U;
+
 struct timetable {
   struct locations {
     timezone_idx_t register_timezone(timezone tz) {