Ah yes, that's true, it must now be a BigDecimal. The initial commit to match up the interfaces had more to do with the fact that the PremiumMoney constructor took a pound amount, but the Money constructor took a penny amount (hence `modified_amount = amount * 100` in the old PremiumMoney constructor). I think the end result of all this is fine, but it does make that previous commit message *slightly* misleading.