This study examines the effect of formal institutions, specifically constitutional provisions, on minority discrimination in Muslim societies. We hypothesize that those Muslim countries in which (political) Islam constitutes an important constraint in the legislative process experience more discrimination against minorities than other (Muslim) countries. In other words, as Islam becomes a constitutionally prescribed source of legislation in Muslim societies, it is expected that subsequent laws will be more likely in violation of basic rights of minorities. In our empirical analysis, we find that where the supremacy of Islam and Shari’a is constitutionally entrenched, religious minorities are indeed likely to face more discrimination. Instrumental variable regressions support our interpretation that this result reflects a causal effect of constitutional rules on social outcomes. We find no evidence that Islam encourages minority discrimination if it is not constitutionalized. Our results confirm the grave dangers entailed in the institutionalization of supreme values.