diff --git a/src/house.h b/src/house.h
--- a/src/house.h
+++ b/src/house.h
@@ -11,7 +11,7 @@
 #define HOUSE_H
 
 #include "cargo_type.h"
-#include "date_type.h"
+#include "timer/timer_game_calendar.h"
 #include "house_type.h"
 #include "newgrf_animation_type.h"
 #include "newgrf_commons.h"
@@ -97,8 +97,8 @@ DECLARE_ENUM_AS_BIT_SET(HouseExtraFlags)
 
 struct HouseSpec {
 	/* Standard properties */
-	Year min_year;                            ///< introduction year of the house
-	Year max_year;                            ///< last year it can be built
+	TimerGameCalendar::Year min_year;         ///< introduction year of the house
+	TimerGameCalendar::Year max_year;         ///< last year it can be built
 	byte population;                          ///< population (Zero on other tiles in multi tile house.)
 	byte removal_cost;                        ///< cost multiplier for removing it
 	StringID building_name;                   ///< building name