We examine whether the relationship between economic inequality and voluntary cooperation is influenced by the quality of local institutions, as proxied by corruption. We use representative data from a large-scale lab-in-the-field public goods experiment with over 1,300 participants across rural Vietnam. Our results show that inequality adversely affects aggregate contributions due to high endowment individuals contributing a significantly smaller share than those with low endowments. This negative effect of inequality on cooperation is stronger in high corruption environments. We find that corruption is associated with pessimistic beliefs about others’ contributions in heterogeneous groups, highlighting the indirect costs of corruption that are understudied in the literature. These findings have implications for public policies aimed at resolving local collective action problems.