Niklas Luhmann held a skeptical view of the role of morality in the modern society. The present paper reassesses this skepticism in view of his early work showing the regime of functional differentiation to be supported by fundamental human rights. Building on this argument, the paper advocates a more positive view of morality which is shown to be related to the sustainability of social systems in their encompassing societal and natural environment. This view is warranted by the overarching Luhmannian theme (...) of the precariousness of system–environment relations. If this view is accepted, Luhmann’s work on fundamental human rights can be read as an illustration of moral problems caused by the overexpansion tendencies of the political system. This argument is shown to connect up with the ideas of Buchanan and Rawls, as well as to fit in with the Luhmannian construct of the dilemma of structure and function. (shrink)