diff --git a/src/timetable_cmd.h b/src/timetable_cmd.h
--- a/src/timetable_cmd.h
+++ b/src/timetable_cmd.h
@@ -11,12 +11,13 @@
 #define TIMETABLE_CMD_H
 
 #include "command_type.h"
+#include "timer/timer_game_calendar.h"
 
 CommandCost CmdChangeTimetable(DoCommandFlag flags, VehicleID veh, VehicleOrderID order_number, ModifyTimetableFlags mtf, uint16 data);
 CommandCost CmdBulkChangeTimetable(DoCommandFlag flags, VehicleID veh, ModifyTimetableFlags mtf, uint16 data);
 CommandCost CmdSetVehicleOnTime(DoCommandFlag flags, VehicleID veh, bool apply_to_group);
 CommandCost CmdAutofillTimetable(DoCommandFlag flags, VehicleID veh, bool autofill, bool preserve_wait_time);
-CommandCost CmdSetTimetableStart(DoCommandFlag flags, VehicleID veh_id, bool timetable_all, Date start_date);
+CommandCost CmdSetTimetableStart(DoCommandFlag flags, VehicleID veh_id, bool timetable_all, TimerGameCalendar::Date start_date);
 
 DEF_CMD_TRAIT(CMD_CHANGE_TIMETABLE,      CmdChangeTimetable,     0, CMDT_ROUTE_MANAGEMENT)
 DEF_CMD_TRAIT(CMD_BULK_CHANGE_TIMETABLE, CmdBulkChangeTimetable, 0, CMDT_ROUTE_MANAGEMENT)