This study examines the effects of formal institutions, specifically constitutions that prescribe Sharia law as a source of legislation, on discrimination against religious minorities. We hypothesize that countries in which the supreme values of Islam are entrenched in the constitution exhibit more discrimination against religious minorities than otherwise comparable countries. In our empirical analysis, we find that religious minorities are indeed likely to face more religious discrimination under Islamic constitutions, even if the relevance of Islam in society is separately taken into account, for example, in terms of the Muslim population share. Instrumental variable regressions support our hypothesis of a causal effect of constitutional rules on de facto social outcomes. However, we find no evidence that Islam encourages discrimination against minorities when it is not entrenched in the constitution. Our results support the grave dangers inherent in the constitutionalization of supreme values.