diff --git a/src/economy.cpp b/src/economy.cpp
--- a/src/economy.cpp
+++ b/src/economy.cpp
@@ -1093,6 +1093,10 @@ void PrepareUnload(Vehicle *front_v)
 	}
 
 	assert(front_v->cargo_payment == NULL);
+	/* One CargoPayment per vehicle and the vehicle limit equals the
+	 * limit in number of CargoPayments. Can't go wrong. */
+	assert_compile(CargoPaymentPool::MAX_SIZE == VehiclePool::MAX_SIZE);
+	assert(CargoPayment::CanAllocateItem());
 	front_v->cargo_payment = new CargoPayment(front_v);
 }