A process for reducing the number of unstable end-groups in a fluorinated polymer is disclosed, said process comprising reacting a fluorinated polymer comprising unstable end-groups with fluorine in the presence of at least one (per)haloolefin comprising at least one carbon-carbon double bond and having at least one fluorine or chlorine atom on either one of the carbon atoms of said double bond. The fluorinated polymer may be selected from those polymers comprising recurring units derived from at least one ethylenically unsaturated fluorinated monomer or from fluorinated polyethers.