The current invention relates to a process for stabilizing a hypophosphite salt, comprising the step of heating the hypophosphite salt at a temperature of between 150 and 370° C. during a sufficient period of time to prevent the formation of a dangerous quantity of phosphine in their application as FR in polymers and a flame retardant polymer composition comprising a polymer and 0.1 to 30 weight percent based on the total weight of the composition of the hypophosphite salt thermally stabilized by the above process.