diff --git a/src/timetable_cmd.cpp b/src/timetable_cmd.cpp
--- a/src/timetable_cmd.cpp
+++ b/src/timetable_cmd.cpp
@@ -306,7 +306,7 @@ CommandCost CmdSetTimetableStart(DoComma
 	if (start_date < 0 || start_date > MAX_DAY) return CMD_ERROR;
 	if (start_date - _date > MAX_TIMETABLE_START_YEARS * DAYS_IN_LEAP_YEAR) return CMD_ERROR;
 	if (_date - start_date > DAYS_IN_LEAP_YEAR) return CMD_ERROR;
-	if (timetable_all && !v->orders->IsCompleteTimetable()) return CMD_ERROR;
+	if (timetable_all && !v->orders->IsCompleteTimetable()) return CommandCost(STR_ERROR_TIMETABLE_INCOMPLETE);
 	if (timetable_all && start_date + total_duration / DAY_TICKS > MAX_DAY) return CMD_ERROR;
 
 	if (flags & DC_EXEC) {