The present invention relates to a process for the preparation of an aqueous dispersion of an anionic polyurethane. According to the invention, a tertiary amine functional urethane polymer or oligomer acts as acid neutralizing agent. The process of the invention comprises the steps of: dispersion of an anionic isocyanate functional polyurethane prepolymer in water in the presence of a tertiary amine functional urethane polymer or oligomer and chain extension of the anionic polyurethane prepolymer with a reactive hydrogen functional material during or after the dispersion in water.