A flame retardant composition is provided which contains at least one phosphate ester containing at least one acidic substance resulting from the process of its manufacture, at least one acidity-reducing hydrotalcite and, optionally, at least one acidity-reducing oxetane. The flame retardant composition is especially useful for addition to resins that are susceptible to hydrolytic degradation such as polyesters and polycarbonates, and to resin blends (alloys) containing one or more of such resins, e.g., a blend of polycarbonate and acrylonitrile butadiene-styrene terpolymer.