diff --git a/src/engine_base.h b/src/engine_base.h
--- a/src/engine_base.h
+++ b/src/engine_base.h
@@ -14,6 +14,7 @@
 #include "vehicle_type.h"
 #include "core/pool_type.hpp"
 #include "newgrf_commons.h"
+#include "timer/timer_game_calendar.h"
 
 struct WagonOverride {
 	std::vector<EngineID> engines;
@@ -35,8 +36,8 @@ extern EnginePool _engine_pool;
 
 struct Engine : EnginePool::PoolItem<&_engine_pool> {
 	std::string name;           ///< Custom name of engine.
-	Date intro_date;            ///< Date of introduction of the engine.
-	Date age;
+	TimerGameCalendar::Date intro_date; ///< Date of introduction of the engine.
+	TimerGameCalendar::Date age;        ///< Age of the engine, in days.
 	uint16 reliability;         ///< Current reliability of the engine.
 	uint16 reliability_spd_dec; ///< Speed of reliability decay between services (per day).
 	uint16 reliability_start;   ///< Initial reliability of the engine.
@@ -123,7 +124,7 @@ struct Engine : EnginePool::PoolItem<&_e
 	uint GetPower() const;
 	uint GetDisplayWeight() const;
 	uint GetDisplayMaxTractiveEffort() const;
-	Date GetLifeLengthInDays() const;
+	TimerGameCalendar::Date GetLifeLengthInDays() const;
 	uint16 GetRange() const;
 	StringID GetAircraftTypeText() const;