This invention relates to the use of a stabilizer which significantly enhances the compatibility of the binder (polymer dispersion) with the liquid ammonium polyphosphate, called APP for short, in a flame-retardant coating composition. In this flame-retardant coating composition, the liquid ammonium polyphosphate functions as active flame retardant. The flame-retardant coating compositions are highly suitable for all kinds of textiles, but also for paper, leather and fibre materials. The purpose of flame retardants is to retard the inflammation of combustible materials, such as plastics, textiles or wood, and to slow down or prevent entirely the spread of flame.