The present paper examines the place of non-Islamic justice in two medieval Islamic political texts, Abū Bakr al-Ṭurṭūshī’s (d. 1126) Lamp of Kings (Sirāj al-Mulūk) and ʿAbd al-Raḥmān Ibn Khaldūn’s (d. 1406) Prolegomena (Muqaddima). By attempting to derive the principles of political justice through reason, and by repudiating claims that normative political values are solely derived from revelation, both thinkers commit to thoroughgoing recognition of non-Islamic forms of justice. As they formulate a pessimistic account of human nature, both contend that the principal objective of political justice is deterrence of innate human lawlessness. And since humans are deemed feeble and corruptible, they may settle for practical political solutions, even if outside the tradition of scripture and revelation. In the final analysis, this rationalist account is juxtaposed to the political aims of certain strands of modern traditionalism, where the role of reason is greatly minimized, if not completely subordinated to revelation. For fundamentalist revivalists, the categories of Islamic and non-Islamic societies intimate a striking opposition between just and unjust societies. While al-Ṭurṭūshī and Ibn Khaldūn also maintain a qualitative difference between Islamic and non-Islamic polities, their conclusions are markedly different from those of the modern traditionalists. The notion of justice they advance, which rests on a pessimistic thesis, results in a more intent recognition of non-Islamic political institutions and laws, irrespective of their creedal origins.