This article examines the extent to which John Rawls could be considered an intellectual ally of ecology and socialism. Although his work offers indispensable resources for conceiving a form of eco-socialism that respects fundamental rights and equal opportunities, as well as a post-growth society, the principle of difference, in some of its formulations, remains ambivalent. The thesis of this article is that this principle remains imbued with a residue of a an efficiency-maximizing logic that can be in tension with socialist egalitarianism on the one hand, and environmental protection on the other. A non-maximising reformulation of the difference principle is therefore proposed, which better distinguishes between the requirements of justice and efficiency, and which is more compatible with equality and collective sobriety.