diff --git a/src/lang/english.txt b/src/lang/english.txt
--- a/src/lang/english.txt
+++ b/src/lang/english.txt
@@ -5110,6 +5110,7 @@ STR_ERROR_NO_BUOY                       
 STR_ERROR_CAN_T_TIMETABLE_VEHICLE                               :{WHITE}Can't timetable vehicle...
 STR_ERROR_TIMETABLE_ONLY_WAIT_AT_STATIONS                       :{WHITE}Vehicles can only wait at stations
 STR_ERROR_TIMETABLE_NOT_STOPPING_HERE                           :{WHITE}This vehicle is not stopping at this station
+STR_ERROR_TIMETABLE_INCOMPLETE                                  :{WHITE}... timetable is incomplete
 
 # Sign related errors
 STR_ERROR_TOO_MANY_SIGNS                                        :{WHITE}... too many signs
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) {
diff --git a/src/timetable_gui.cpp b/src/timetable_gui.cpp
--- a/src/timetable_gui.cpp
+++ b/src/timetable_gui.cpp
@@ -572,7 +572,7 @@ struct TimetableWindow : Window {
 			}
 
 			case WID_VT_START_DATE: // Change the date that the timetable starts.
-				ShowSetDateWindow(this, v->index, _date, _cur_year, _cur_year + MAX_TIMETABLE_START_YEARS, ChangeTimetableStartCallback, reinterpret_cast<void *>(static_cast<uintptr_t>(v->orders->IsCompleteTimetable() && _ctrl_pressed)));
+				ShowSetDateWindow(this, v->index, _date, _cur_year, _cur_year + MAX_TIMETABLE_START_YEARS, ChangeTimetableStartCallback, reinterpret_cast<void *>(static_cast<uintptr_t>(_ctrl_pressed)));
 				break;
 
 			case WID_VT_CHANGE_TIME: { // "Wait For" button.