In customs preference schemes, prison labour is primarily viewed as unfair competition, to be rejected out of hand. This form of employment can, however, be understood differently, notably by considering the conditions under which it may constitute decent work, and by seeing it as a tool for rehabilitation. Following an in-depth legal analysis, in which they compare the relevant standards of the ILO to EU and WTO customs regulations in the light of the capability approach, the authors call for the development of a set of rules drawing on several branches of law relating to prison labour.