Many urban areas use non-cumulative zoning – zoning exclusive to one use (typically manufacturing) that prohibits other uses even if those uses are considered less noxious. Proponents of this zoning claim that it is necessary to reduce the degree to which urban manufacturers are held responsible for nuisance. This article argues that this justification is flawed, and alternative means could achieve the same ends with fewer costs. Non-cumulative zoning is really a subsidy to manufacturers, reducing their land cost by eliminating potential competitors for land. This subsidy cannot be justified because non-cumulative zoning is unlikely to achieve either local or broader social efficiency.