What role does religion play in preventing civil war from recurring? Politicians have proposed that when warring groups share the same religion, achieving a durable peace will be easier. We test this hypothesis empirically using a large-n sample of all ethnic civil wars that began and ended between 1950 and 2006, and a measure of co-religiosity between the ethnic group in power and the main opposition group. The analysis shows that there is no positive relationship between co-religiosity and the duration of post-civil war peace, showing that sharing the same religion may not help to bring about peace following an ethnic civil war. To the contrary, the closer religious ties, the less likely it is that peace will last after the end of the conflict, and the higher the risk that conflict will recur.