diff --git a/src/newgrf_object.cpp b/src/newgrf_object.cpp
--- a/src/newgrf_object.cpp
+++ b/src/newgrf_object.cpp
@@ -361,7 +361,7 @@ static const SpriteGroup *GetObjectSprit
 /**
  * Returns a resolver object to be used with feature 0F spritegroups.
  */
-static void NewObjectResolver(ResolverObject *res, const ObjectSpec *spec, const Object *o, TileIndex tile, uint8 view = 0)
+static void NewObjectResolver(ResolverObject *res, const ObjectSpec *spec, Object *o, TileIndex tile, uint8 view = 0)
 {
 	res->GetRandomBits = ObjectGetRandomBits;
 	res->GetTriggers   = ObjectGetTriggers;
@@ -395,7 +395,7 @@ static void NewObjectResolver(ResolverOb
  * @param view     The view of the object (only used when o == NULL).
  * @return The result of the callback.
  */
-uint16 GetObjectCallback(CallbackID callback, uint32 param1, uint32 param2, const ObjectSpec *spec, const Object *o, TileIndex tile, uint8 view)
+uint16 GetObjectCallback(CallbackID callback, uint32 param1, uint32 param2, const ObjectSpec *spec, Object *o, TileIndex tile, uint8 view)
 {
 	ResolverObject object;
 	NewObjectResolver(&object, spec, o, tile, view);
@@ -444,7 +444,7 @@ static void DrawTileLayout(const TileInf
 void DrawNewObjectTile(TileInfo *ti, const ObjectSpec *spec)
 {
 	ResolverObject object;
-	const Object *o = Object::GetByTile(ti->tile);
+	Object *o = Object::GetByTile(ti->tile);
 	NewObjectResolver(&object, spec, o, ti->tile);
 
 	const SpriteGroup *group = SpriteGroup::Resolve(GetObjectSpriteGroup(spec, o), &object);
diff --git a/src/newgrf_object.h b/src/newgrf_object.h
--- a/src/newgrf_object.h
+++ b/src/newgrf_object.h
@@ -95,7 +95,7 @@ typedef NewGRFClass<ObjectSpec, ObjectCl
 /** Mapping of purchase for objects. */
 static const CargoID CT_PURCHASE_OBJECT = 1;
 
-uint16 GetObjectCallback(CallbackID callback, uint32 param1, uint32 param2, const ObjectSpec *spec, const Object *o, TileIndex tile, uint8 view = 0);
+uint16 GetObjectCallback(CallbackID callback, uint32 param1, uint32 param2, const ObjectSpec *spec, Object *o, TileIndex tile, uint8 view = 0);
 
 void DrawNewObjectTile(TileInfo *ti, const ObjectSpec *spec);
 void DrawNewObjectTileInGUI(int x, int y, const ObjectSpec *spec, uint8 view);
diff --git a/src/newgrf_spritegroup.h b/src/newgrf_spritegroup.h
--- a/src/newgrf_spritegroup.h
+++ b/src/newgrf_spritegroup.h
@@ -371,7 +371,7 @@ struct ResolverObject {
 			TileIndex tile;                ///< Tile for the callback, only valid for airporttile callbacks.
 		} airport;
 		struct {
-			const struct Object *o;        ///< The object the callback is ran for.
+			struct Object *o;              ///< The object the callback is ran for.
 			TileIndex tile;                ///< The tile related to the object.
 			uint8 view;                    ///< The view of the object.
 		} object;