The principle of proportionality has gained widespread adherence in the modern retributively-dominated era of penal theory. It has often been held that, if one subscribes to a retributivist theory, then one is also committed to proportionality in punishment (or at least to proportionately-determined upper punishment constraints). In the present article, this assumption is challenged. It is shown that the inference from the fact that one offender has committed a more serious crime than another offender, to the conclusion that this offender should be punished more severely than the other, presupposes the satisfaction of two conditions: The Necessity Requirement and the Sufficiency Requirement. It is argued that modern expressionist accounts of retributivism fail to satisfy these requirements. Moreover, it is suggested that the satisfaction of these requirements constitutes a challenge for other retributivist theories. In so far as this is the case, the inference from retributivism to proportionality will be blocked.