diff --git a/src/economy.cpp b/src/economy.cpp
--- a/src/economy.cpp
+++ b/src/economy.cpp
@@ -1165,7 +1165,7 @@ static void LoadUnloadVehicle(Vehicle *v
 		byte load_amount = e->info.load_amount;
 
 		/* The default loadamount for mail is 1/4 of the load amount for passengers */
-		if (v->type == VEH_AIRCRAFT && !Aircraft::From(v)->IsNormalAircraft()) load_amount = (load_amount + 3) / 4;
+		if (v->type == VEH_AIRCRAFT && !Aircraft::From(v)->IsNormalAircraft()) load_amount = CeilDiv(load_amount, 4);
 
 		if (_settings_game.order.gradual_loading && HasBit(e->info.callback_mask, CBM_VEHICLE_LOAD_AMOUNT)) {
 			uint16 cb_load_amount = GetVehicleCallback(CBID_VEHICLE_LOAD_AMOUNT, 0, 0, v->engine_type, v);