If local public goods exhibit spillovers and regions are sufficiently symmetric, decentralization implies underprovision, whereas cooperative centralization is associated with strict Pareto-improvement. This classic inference rests on two assumptions: local politicians are delegated sincerely and never provide voluntary transfers to the other regions. We abandon these assumptions in a setup of two symmetric regions with imperfect complementarity between local public goods. For this particular aggregation, non-cooperative decentralization can achieve the social optimum, whereas cooperative centralization cannot.