diff --git a/src/cheat_gui.cpp b/src/cheat_gui.cpp
index d226591add..477fa3d748 100644
--- a/src/cheat_gui.cpp
+++ b/src/cheat_gui.cpp
@@ -113,7 +113,7 @@ static int32_t ClickChangeDateCheat(int32_t new_value, int32_t)
 	/* If not using wallclock units, we keep economy date in sync with calendar date and must change it also. */
 	if (!TimerGameEconomy::UsingWallclockUnits()) {
 		/* Keep economy and calendar dates synced. */
-		TimerGameEconomy::Date new_economy_date = new_calendar_date.base();
+		TimerGameEconomy::Date new_economy_date{new_calendar_date.base()};
 
 		/* Shift cached dates before we change the date. */
 		for (auto v : Vehicle::Iterate()) v->ShiftDates(new_economy_date - TimerGameEconomy::date);
diff --git a/src/engine.cpp b/src/engine.cpp
index 6e920d87f6..f2516ec505 100644
--- a/src/engine.cpp
+++ b/src/engine.cpp
@@ -443,7 +443,7 @@ uint Engine::GetDisplayMaxTractiveEffort() const
 TimerGameCalendar::Date Engine::GetLifeLengthInDays() const
 {
 	/* Assume leap years; this gives the player a bit more than the given amount of years, but never less. */
-	return (this->info.lifelength + _settings_game.vehicle.extend_vehicle_life).base() * CalendarTime::DAYS_IN_LEAP_YEAR;
+	return TimerGameCalendar::Date{(this->info.lifelength + _settings_game.vehicle.extend_vehicle_life).base() * CalendarTime::DAYS_IN_LEAP_YEAR};
 }
 
 /**
@@ -1320,7 +1320,7 @@ bool IsEngineRefittable(EngineID engine)
  */
 void CheckEngines()
 {
-	TimerGameCalendar::Date min_date = INT32_MAX;
+	TimerGameCalendar::Date min_date{INT32_MAX};
 
 	for (const Engine *e : Engine::Iterate()) {
 		if (!e->IsEnabled()) continue;
diff --git a/src/linkgraph/linkgraphschedule.cpp b/src/linkgraph/linkgraphschedule.cpp
index 72f28a3270..d9bee368d3 100644
--- a/src/linkgraph/linkgraphschedule.cpp
+++ b/src/linkgraph/linkgraphschedule.cpp
@@ -202,7 +202,7 @@ void AfterLoad_LinkGraphPauseControl()
 void OnTick_LinkGraph()
 {
 	if (TimerGameEconomy::date_fract != LinkGraphSchedule::SPAWN_JOIN_TICK) return;
-	TimerGameEconomy::Date offset = TimerGameEconomy::date.base() % (_settings_game.linkgraph.recalc_interval / EconomyTime::SECONDS_PER_DAY);
+	TimerGameEconomy::Date offset{TimerGameEconomy::date.base() % (_settings_game.linkgraph.recalc_interval / EconomyTime::SECONDS_PER_DAY)};
 	if (offset == 0) {
 		LinkGraphSchedule::instance.SpawnNext();
 	} else if (offset == (_settings_game.linkgraph.recalc_interval / EconomyTime::SECONDS_PER_DAY) / 2) {
diff --git a/src/misc.cpp b/src/misc.cpp
index 72701ff23c..ad44417367 100644
--- a/src/misc.cpp
+++ b/src/misc.cpp
@@ -112,10 +112,10 @@ void InitializeGame(uint size_x, uint size_y, bool reset_date, bool reset_settin
 
 		if (TimerGameEconomy::UsingWallclockUnits()) {
 			/* If using wallclock units, start at year 1. */
-			TimerGameEconomy::SetDate(TimerGameEconomy::ConvertYMDToDate(1, 0, 1), 0);
+			TimerGameEconomy::SetDate(TimerGameEconomy::ConvertYMDToDate(TimerGameEconomy::Year{1}, 0, 1), 0);
 		} else {
 			/* Otherwise, we always keep the economy date synced with the calendar date. */
-			TimerGameEconomy::SetDate(new_date.base(), 0);
+			TimerGameEconomy::SetDate(TimerGameEconomy::Date{new_date.base()}, 0);
 		}
 		InitializeOldNames();
 	}
diff --git a/src/newgrf.cpp b/src/newgrf.cpp
index bae0c25a96..1382b3731f 100644
--- a/src/newgrf.cpp
+++ b/src/newgrf.cpp
@@ -2264,7 +2264,7 @@ static ChangeInfoResult BridgeChangeInfo(uint brid, int numinfo, int prop, ByteR
 			case 0x08: { // Year of availability
 				/* We treat '0' as always available */
 				uint8_t year = buf.ReadByte();
-				bridge->avail_year = (year > 0 ? CalendarTime::ORIGINAL_BASE_YEAR + year : 0);
+				bridge->avail_year = (year > 0 ? CalendarTime::ORIGINAL_BASE_YEAR + year : TimerGameCalendar::Year{});
 				break;
 			}
 
@@ -2856,7 +2856,7 @@ static ChangeInfoResult GlobalVarChangeInfo(uint gvid, int numinfo, int prop, By
 
 			case 0x0F: { //  Euro introduction dates
 				uint curidx = GetNewgrfCurrencyIdConverted(gvid + i);
-				TimerGameCalendar::Year year_euro = buf.ReadWord();
+				TimerGameCalendar::Year year_euro{buf.ReadWord()};
 
 				if (curidx < CURRENCY_END) {
 					_currency_specs[curidx].to_euro = year_euro;
diff --git a/src/saveload/afterload.cpp b/src/saveload/afterload.cpp
index 106c279b18..5d3c327789 100644
--- a/src/saveload/afterload.cpp
+++ b/src/saveload/afterload.cpp
@@ -740,7 +740,7 @@ bool AfterLoadGame()
 
 	/* Update economy year. If we don't have a separate economy date saved, follow the calendar date. */
 	if (IsSavegameVersionBefore(SLV_ECONOMY_DATE)) {
-		TimerGameEconomy::SetDate(TimerGameCalendar::date.base(), TimerGameCalendar::date_fract);
+		TimerGameEconomy::SetDate(TimerGameEconomy::Date{TimerGameCalendar::date.base()}, TimerGameCalendar::date_fract);
 	} else {
 		TimerGameEconomy::SetDate(TimerGameEconomy::date, TimerGameEconomy::date_fract);
 	}
@@ -1965,7 +1965,7 @@ bool AfterLoadGame()
 
 			/* Replace "house construction year" with "house age" */
 			if (IsTileType(t, MP_HOUSE) && IsHouseCompleted(t)) {
-				t.m5() = ClampTo<uint8_t>(TimerGameCalendar::year - (t.m5() + CalendarTime::ORIGINAL_BASE_YEAR));
+				t.m5() = ClampTo<uint8_t>(TimerGameCalendar::year - (CalendarTime::ORIGINAL_BASE_YEAR + t.m5()));
 			}
 		}
 	}
diff --git a/src/saveload/industry_sl.cpp b/src/saveload/industry_sl.cpp
index 73479ce2a0..409631911b 100644
--- a/src/saveload/industry_sl.cpp
+++ b/src/saveload/industry_sl.cpp
@@ -39,7 +39,7 @@ public:
 	{
 		SlIndustryAccepted::old_cargo.fill(INVALID_CARGO);
 		SlIndustryAccepted::old_waiting.fill(0);
-		SlIndustryAccepted::old_last_accepted.fill(0);
+		SlIndustryAccepted::old_last_accepted.fill(TimerGameEconomy::Date{});
 	}
 };
 
diff --git a/src/saveload/oldloader_sl.cpp b/src/saveload/oldloader_sl.cpp
index 064f53d5fa..a8b7a452e4 100644
--- a/src/saveload/oldloader_sl.cpp
+++ b/src/saveload/oldloader_sl.cpp
@@ -387,7 +387,7 @@ static bool FixTTOEngines()
 		for (uint i = 0; i < lengthof(_orig_aircraft_vehicle_info); i++, j++) new (GetTempDataEngine(j)) Engine(VEH_AIRCRAFT, i);
 	}
 
-	TimerGameCalendar::Date aging_date = std::min(TimerGameCalendar::date + CalendarTime::DAYS_TILL_ORIGINAL_BASE_YEAR, TimerGameCalendar::ConvertYMDToDate(2050, 0, 1));
+	TimerGameCalendar::Date aging_date = std::min(TimerGameCalendar::date + CalendarTime::DAYS_TILL_ORIGINAL_BASE_YEAR, TimerGameCalendar::ConvertYMDToDate(TimerGameCalendar::Year{2050}, 0, 1));
 	TimerGameCalendar::YearMonthDay aging_ymd = TimerGameCalendar::ConvertDateToYMD(aging_date);
 
 	for (EngineID i = 0; i < 256; i++) {
diff --git a/src/saveload/vehicle_sl.cpp b/src/saveload/vehicle_sl.cpp
index 22c4dbf105..31d0a39c6c 100644
--- a/src/saveload/vehicle_sl.cpp
+++ b/src/saveload/vehicle_sl.cpp
@@ -396,7 +396,7 @@ void AfterLoadVehiclesPhase1(bool part_of_load)
 				/* If the start date is 0, the vehicle is not waiting to start and can be ignored. */
 				if (v->timetable_start == 0) continue;
 
-				v->timetable_start = GetStartTickFromDate(v->timetable_start);
+				v->timetable_start = GetStartTickFromDate(TimerGameEconomy::Date(v->timetable_start));
 			}
 		}
 
diff --git a/src/script/api/script_date.cpp b/src/script/api/script_date.cpp
index cffa57fea9..3ff39b6232 100644
--- a/src/script/api/script_date.cpp
+++ b/src/script/api/script_date.cpp
@@ -29,7 +29,7 @@
 {
 	if (date < 0) return DATE_INVALID;
 
-	::TimerGameEconomy::YearMonthDay ymd = ::TimerGameEconomy::ConvertDateToYMD(date);
+	::TimerGameEconomy::YearMonthDay ymd = ::TimerGameEconomy::ConvertDateToYMD(::TimerGameEconomy::Date{date});
 	return ymd.year.base();
 }
 
@@ -37,7 +37,7 @@
 {
 	if (date < 0) return DATE_INVALID;
 
-	::TimerGameEconomy::YearMonthDay ymd = ::TimerGameEconomy::ConvertDateToYMD(date);
+	::TimerGameEconomy::YearMonthDay ymd = ::TimerGameEconomy::ConvertDateToYMD(::TimerGameEconomy::Date{date});
 	return ymd.month + 1;
 }
 
@@ -45,7 +45,7 @@
 {
 	if (date < 0) return DATE_INVALID;
 
-	::TimerGameEconomy::YearMonthDay ymd = ::TimerGameEconomy::ConvertDateToYMD(date);
+	::TimerGameEconomy::YearMonthDay ymd = ::TimerGameEconomy::ConvertDateToYMD(::TimerGameEconomy::Date{date});
 	return ymd.day;
 }
 
@@ -53,9 +53,11 @@
 {
 	if (month < 1 || month > 12) return DATE_INVALID;
 	if (day_of_month < 1 || day_of_month > 31) return DATE_INVALID;
-	if (year < 0 || year > EconomyTime::MAX_YEAR) return DATE_INVALID;
 
-	return (ScriptDate::Date)::TimerGameEconomy::ConvertYMDToDate(year, month - 1, day_of_month).base();
+	::TimerGameEconomy::Year timer_year{ClampTo<int32_t>(year)};
+	if (timer_year < EconomyTime::MIN_YEAR || timer_year > EconomyTime::MAX_YEAR) return DATE_INVALID;
+
+	return static_cast<ScriptDate::Date>(::TimerGameEconomy::ConvertYMDToDate(timer_year, month - 1, day_of_month).base());
 }
 
 /* static */ SQInteger ScriptDate::GetSystemTime()
diff --git a/src/script/api/script_story_page.cpp b/src/script/api/script_story_page.cpp
index 2471d35745..f664c7771f 100644
--- a/src/script/api/script_story_page.cpp
+++ b/src/script/api/script_story_page.cpp
@@ -196,7 +196,7 @@ static inline bool StoryPageElementTypeRequiresText(StoryPageElementType type)
 	EnforcePrecondition(false, IsValidStoryPage(story_page_id));
 	EnforceDeityMode(false);
 
-	return ScriptObject::Command<CMD_SET_STORY_PAGE_DATE>::Do(story_page_id, date);
+	return ScriptObject::Command<CMD_SET_STORY_PAGE_DATE>::Do(story_page_id, ::TimerGameCalendar::Date{date});
 }
 
 
diff --git a/src/script/api/script_subsidy.cpp b/src/script/api/script_subsidy.cpp
index 02f283d87a..e8d2905cb6 100644
--- a/src/script/api/script_subsidy.cpp
+++ b/src/script/api/script_subsidy.cpp
@@ -58,7 +58,7 @@
 	ymd.day = 1;
 	auto m = ymd.month + ::Subsidy::Get(subsidy_id)->remaining;
 	ymd.month = (m - 1) % 12 + 1;
-	ymd.year += (m - 1) / 12;
+	ymd.year += TimerGameEconomy::Year{(m - 1) / 12};
 
 	return (ScriptDate::Date)TimerGameEconomy::ConvertYMDToDate(ymd.year, ymd.month, ymd.day).base();
 }
diff --git a/src/settings_gui.cpp b/src/settings_gui.cpp
index c4c660bf31..a88195043e 100644
--- a/src/settings_gui.cpp
+++ b/src/settings_gui.cpp
@@ -3151,7 +3151,7 @@ struct CustomCurrencyWindow : Window {
 				break;
 
 			case WID_CC_YEAR: { // Year to switch to euro
-				TimerGameCalendar::Year val = atoi(str->c_str());
+				TimerGameCalendar::Year val{atoi(str->c_str())};
 
 				GetCustomCurrency().to_euro = (val < MIN_EURO_YEAR ? CF_NOEURO : std::min(val, CalendarTime::MAX_YEAR));
 				break;
diff --git a/src/settings_table.cpp b/src/settings_table.cpp
index 2ebb856d41..95ecac46f2 100644
--- a/src/settings_table.cpp
+++ b/src/settings_table.cpp
@@ -604,7 +604,7 @@ static void ChangeTimekeepingUnits(int32_t)
 
 		if (TimerGameEconomy::UsingWallclockUnits()) {
 			/* If the new mode is wallclock units, set the economy year back to 1. */
-			new_economy_date = TimerGameEconomy::ConvertYMDToDate(1, 0, 1);
+			new_economy_date = TimerGameEconomy::ConvertYMDToDate(TimerGameEconomy::Year{1}, 0, 1);
 			new_economy_date_fract = 0;
 		} else {
 			/* If the new mode is calendar units, sync the economy year with the calendar year. */
diff --git a/src/timer/timer_game_calendar.cpp b/src/timer/timer_game_calendar.cpp
index 30f938464c..34300ae2a7 100644
--- a/src/timer/timer_game_calendar.cpp
+++ b/src/timer/timer_game_calendar.cpp
@@ -70,7 +70,7 @@ uint16_t TimerGameCalendar::sub_date_fract = {};
 	TimerGameCalendar::date = date;
 	TimerGameCalendar::date_fract = fract;
 	TimerGameCalendar::YearMonthDay ymd = TimerGameCalendar::ConvertDateToYMD(date);
-	TimerGameCalendar::year = ymd.year;
+	TimerGameCalendar::year = TimerGameCalendar::Year{ymd.year};
 	TimerGameCalendar::month = ymd.month;
 }
 
@@ -157,10 +157,8 @@ bool TimerManager<TimerGameCalendar>::Elapsed([[maybe_unused]] TimerGameCalendar
 
 	/* If we reached the maximum year, decrement dates by a year. */
 	if (TimerGameCalendar::year == CalendarTime::MAX_YEAR + 1) {
-		int days_this_year;
-
 		TimerGameCalendar::year--;
-		days_this_year = TimerGameCalendar::IsLeapYear(TimerGameCalendar::year) ? CalendarTime::DAYS_IN_LEAP_YEAR : CalendarTime::DAYS_IN_YEAR;
+		TimerGameCalendar::Date days_this_year{TimerGameCalendar::IsLeapYear(TimerGameCalendar::year) ? CalendarTime::DAYS_IN_LEAP_YEAR : CalendarTime::DAYS_IN_YEAR};
 		TimerGameCalendar::date -= days_this_year;
 	}
 
diff --git a/src/timer/timer_game_common.cpp b/src/timer/timer_game_common.cpp
index 01b9a1a5a3..ff263979c4 100644
--- a/src/timer/timer_game_common.cpp
+++ b/src/timer/timer_game_common.cpp
@@ -68,28 +68,28 @@ template <class T>
 	 */
 
 	/* There are 97 leap years in 400 years */
-	Year yr = 400 * (date.base() / (TimerGameConst<T>::DAYS_IN_YEAR * 400 + 97));
+	Year yr{400 * (date.base() / (TimerGameConst<T>::DAYS_IN_YEAR * 400 + 97))};
 	int rem = date.base() % (TimerGameConst<T>::DAYS_IN_YEAR * 400 + 97);
 
 	if (rem >= TimerGameConst<T>::DAYS_IN_YEAR * 100 + 25) {
 		/* There are 25 leap years in the first 100 years after
 		 * every 400th year, as every 400th year is a leap year */
-		yr += 100;
+		yr += Year{100};
 		rem -= TimerGameConst<T>::DAYS_IN_YEAR * 100 + 25;
 
 		/* There are 24 leap years in the next couple of 100 years */
-		yr += 100 * (rem / (TimerGameConst<T>::DAYS_IN_YEAR * 100 + 24));
+		yr += Year{100 * (rem / (TimerGameConst<T>::DAYS_IN_YEAR * 100 + 24))};
 		rem = (rem % (TimerGameConst<T>::DAYS_IN_YEAR * 100 + 24));
 	}
 
 	if (!IsLeapYear(yr) && rem >= TimerGameConst<T>::DAYS_IN_YEAR * 4) {
 		/* The first 4 year of the century are not always a leap year */
-		yr += 4;
+		yr += Year{4};
 		rem -= TimerGameConst<T>::DAYS_IN_YEAR * 4;
 	}
 
 	/* There is 1 leap year every 4 years */
-	yr += 4 * (rem / (TimerGameConst<T>::DAYS_IN_YEAR * 4 + 1));
+	yr += Year{4 * (rem / (TimerGameConst<T>::DAYS_IN_YEAR * 4 + 1))};
 	rem = rem % (TimerGameConst<T>::DAYS_IN_YEAR * 4 + 1);
 
 	/* The last (max 3) years to account for; the first one
diff --git a/src/timer/timer_game_common.h b/src/timer/timer_game_common.h
index 8ab619e51f..ca6b7e13fa 100644
--- a/src/timer/timer_game_common.h
+++ b/src/timer/timer_game_common.h
@@ -77,7 +77,7 @@ public:
 	static constexpr Year DateToYear(Date date)
 	{
 		/* Hardcode the number of days in a year because we can't access CalendarTime from here. */
-		return date.base() / 366;
+		return Year{date.base() / 366};
 	}
 
 	/**
@@ -88,10 +88,10 @@ public:
 	static constexpr Date DateAtStartOfYear(Year year)
 	{
 		int32_t year_as_int = year.base();
-		uint number_of_leap_years = (year == 0) ? 0 : ((year_as_int - 1) / 4 - (year_as_int - 1) / 100 + (year_as_int - 1) / 400 + 1);
+		int32_t number_of_leap_years = (year == 0) ? 0 : ((year_as_int - 1) / 4 - (year_as_int - 1) / 100 + (year_as_int - 1) / 400 + 1);
 
 		/* Hardcode the number of days in a year because we can't access CalendarTime from here. */
-		return (365 * year_as_int) + number_of_leap_years;
+		return Date{(365 * year_as_int) + number_of_leap_years};
 	}
 
 	enum Trigger {
diff --git a/src/timer/timer_game_economy.cpp b/src/timer/timer_game_economy.cpp
index cd78aa74af..6eac8c7be1 100644
--- a/src/timer/timer_game_economy.cpp
+++ b/src/timer/timer_game_economy.cpp
@@ -70,7 +70,7 @@ TimerGameEconomy::DateFract TimerGameEconomy::date_fract = {};
 
 	/* If we're using wallclock units, economy months have 30 days and an economy year has 360 days. */
 	const int total_months = (year.base() * EconomyTime::MONTHS_IN_YEAR) + month;
-	return (total_months * EconomyTime::DAYS_IN_ECONOMY_MONTH) + day - 1; // Day is 1-indexed but Date is 0-indexed, hence the - 1.
+	return TimerGameEconomy::Date{(total_months * EconomyTime::DAYS_IN_ECONOMY_MONTH) + day - 1}; // Day is 1-indexed but Date is 0-indexed, hence the - 1.
 }
 
 /**
@@ -179,13 +179,11 @@ bool TimerManager<TimerGameEconomy>::Elapsed([[maybe_unused]] TimerGameEconomy::
 
 	/* check if we reached the maximum year, decrement dates by a year */
 	if (TimerGameEconomy::year == EconomyTime::MAX_YEAR + 1) {
-		int days_this_year;
-
 		TimerGameEconomy::year--;
-		days_this_year = TimerGameEconomy::IsLeapYear(TimerGameEconomy::year) ? EconomyTime::DAYS_IN_LEAP_YEAR : EconomyTime::DAYS_IN_YEAR;
-		TimerGameEconomy::date -= days_this_year;
-		for (Vehicle *v : Vehicle::Iterate()) v->ShiftDates(-days_this_year);
-		for (LinkGraph *lg : LinkGraph::Iterate()) lg->ShiftDates(-days_this_year);
+		int days_this_year = TimerGameEconomy::IsLeapYear(TimerGameEconomy::year) ? EconomyTime::DAYS_IN_LEAP_YEAR : EconomyTime::DAYS_IN_YEAR;
+		TimerGameEconomy::date -= TimerGameEconomy::Date{days_this_year};
+		for (Vehicle *v : Vehicle::Iterate()) v->ShiftDates(TimerGameEconomy::Date{-days_this_year});
+		for (LinkGraph *lg : LinkGraph::Iterate()) lg->ShiftDates(TimerGameEconomy::Date{-days_this_year});
 	}
 
 	return true;
diff --git a/src/toolbar_gui.cpp b/src/toolbar_gui.cpp
index d2a46b349b..91d7b470df 100644
--- a/src/toolbar_gui.cpp
+++ b/src/toolbar_gui.cpp
@@ -1113,7 +1113,7 @@ void SetStartingYear(TimerGameCalendar::Year year)
 {
 	_settings_game.game_creation.starting_year = Clamp(year, CalendarTime::MIN_YEAR, CalendarTime::MAX_YEAR);
 	TimerGameCalendar::Date new_calendar_date = TimerGameCalendar::ConvertYMDToDate(_settings_game.game_creation.starting_year, 0, 1);
-	TimerGameEconomy::Date new_economy_date = new_calendar_date.base();
+	TimerGameEconomy::Date new_economy_date{new_calendar_date.base()};
 
 	/* We must set both Calendar and Economy dates to keep them in sync. Calendar first. */
 	TimerGameCalendar::SetDate(new_calendar_date, 0);
diff --git a/src/town_cmd.cpp b/src/town_cmd.cpp
index 848cc13aee..947796fe8e 100644
--- a/src/town_cmd.cpp
+++ b/src/town_cmd.cpp
@@ -998,7 +998,7 @@ static TimerGameCalendar::Date GetTownRoadTypeFirstIntroductionDate()
 		best = rti;
 	}
 
-	if (best == nullptr) return INT32_MAX;
+	if (best == nullptr) return TimerGameCalendar::Date(INT32_MAX);
 	return best->introduction_date;
 }
 
diff --git a/src/town_map.h b/src/town_map.h
index aae94676ac..6cd041643a 100644
--- a/src/town_map.h
+++ b/src/town_map.h
@@ -249,7 +249,7 @@ inline void IncrementHouseAge(Tile t)
 inline TimerGameCalendar::Year GetHouseAge(Tile t)
 {
 	assert(IsTileType(t, MP_HOUSE));
-	return IsHouseCompleted(t) ? t.m5() : 0;
+	return TimerGameCalendar::Year{IsHouseCompleted(t) ? t.m5() : 0};
 }
 
 /**
diff --git a/src/vehicle.cpp b/src/vehicle.cpp
index aecc7138f7..06876853d9 100644
--- a/src/vehicle.cpp
+++ b/src/vehicle.cpp
@@ -1446,7 +1446,7 @@ void AgeVehicle(Vehicle *v)
 
 	auto age = v->age - v->max_age;
 	for (int32_t i = 0; i <= 4; i++) {
-		if (age == TimerGameCalendar::DateAtStartOfYear(i)) {
+		if (age == TimerGameCalendar::DateAtStartOfYear(TimerGameCalendar::Year{i})) {
 			v->reliability_spd_dec <<= 1;
 			break;
 		}
@@ -1467,11 +1467,11 @@ void AgeVehicle(Vehicle *v)
 	if (EngineHasReplacementForCompany(c, v->engine_type, v->group_id)) return;
 
 	StringID str;
-	if (age == TimerGameCalendar::DateAtStartOfYear(-1)) {
+	if (age == TimerGameCalendar::DateAtStartOfYear(TimerGameCalendar::Year{-1})) {
 		str = STR_NEWS_VEHICLE_IS_GETTING_OLD;
-	} else if (age == TimerGameCalendar::DateAtStartOfYear(0)) {
+	} else if (age == TimerGameCalendar::DateAtStartOfYear(TimerGameCalendar::Year{0})) {
 		str = STR_NEWS_VEHICLE_IS_GETTING_VERY_OLD;
-	} else if (age > TimerGameCalendar::DateAtStartOfYear(0) && (age.base() % CalendarTime::DAYS_IN_LEAP_YEAR) == 0) {
+	} else if (age > TimerGameCalendar::DateAtStartOfYear(TimerGameCalendar::Year{0}) && (age.base() % CalendarTime::DAYS_IN_LEAP_YEAR) == 0) {
 		str = STR_NEWS_VEHICLE_IS_GETTING_VERY_OLD_AND;
 	} else {
 		return;