diff --git a/src/object_base.h b/src/object_base.h
--- a/src/object_base.h
+++ b/src/object_base.h
@@ -14,7 +14,7 @@
 #include "object_type.h"
 #include "tilearea_type.h"
 #include "town_type.h"
-#include "date_type.h"
+#include "timer/timer_game_calendar.h"
 
 typedef Pool<Object, ObjectID, 64, 0xFF0000> ObjectPool;
 extern ObjectPool _object_pool;
@@ -24,7 +24,7 @@ struct Object : ObjectPool::PoolItem<&_o
 	ObjectType type;    ///< Type of the object
 	Town *town;         ///< Town the object is built in
 	TileArea location;  ///< Location of the object
-	Date build_date;    ///< Date of construction
+	TimerGameCalendar::Date build_date; ///< Date of construction
 	byte colour;        ///< Colour of the object, for display purpose
 	byte view;          ///< The view setting for this object