diff --git a/src/ground_vehicle.hpp b/src/ground_vehicle.hpp
--- a/src/ground_vehicle.hpp
+++ b/src/ground_vehicle.hpp
@@ -231,9 +231,9 @@ struct GroundVehicle : public Specialize
 	 * @param update_delta Indicates to also update the delta.
 	 * @return Old height of the vehicle.
 	 */
-	inline byte UpdateInclination(bool new_tile, bool update_delta)
+	inline int UpdateInclination(bool new_tile, bool update_delta)
 	{
-		byte old_z = this->z_pos;
+		int old_z = this->z_pos;
 
 		if (new_tile) {
 			this->UpdateZPositionAndInclination();
diff --git a/src/roadveh_cmd.cpp b/src/roadveh_cmd.cpp
--- a/src/roadveh_cmd.cpp
+++ b/src/roadveh_cmd.cpp
@@ -847,7 +847,7 @@ static void RoadVehCheckOvertake(RoadVeh
 	v->overtaking = RVSB_DRIVE_SIDE;
 }
 
-static void RoadZPosAffectSpeed(RoadVehicle *v, byte old_z)
+static void RoadZPosAffectSpeed(RoadVehicle *v, int old_z)
 {
 	if (old_z == v->z_pos || _settings_game.vehicle.roadveh_acceleration_model != AM_ORIGINAL) return;