Reliable institutions, i.e., institutions that live up to the norms that agents expect them to keep foster cooperative behavior. We experimentally confirm this hypothesis in a public goods game with a salient norm that cooperation was socially demanded and corruption ought not to occur. When nevertheless corruption attempts came up, groups that were told that ‘the system’ had fended off the attempts made considerably higher contributions to the public good than groups that learned that attempts only did not affect their payoffs or that were not exposed to corruption at all.