Suppose we adhere to some sort of retributive theory of punishment, that “the punishment should fit the crime.” Suppose further that Eli is convicted of murder and sentenced to 15-20 years in prison, the maximum permissible under the sentencing guidelines at the time of the murder (based on a retributive judgment that 15-20 years is just). Now suppose that officials in the system correctly realize that the principles of just punishment require a sentence of 25-30 years in prison (‘correctly’ being stipulated for the hypo). Is it wrong for the system to alter Eli’s punishment, increasing it to fit the correct retributive calculation? Is it unfair? If so, why? What values usually underlie our judgments condemning retroactive law-making? Do they apply to cases of retrospective increases in punishment?