The present invention relates to a process for producing a propylene polymer, such as a propylene homopolymer, a propylene-ethylene random copolymer or a heterophasic propylene copolymer using a specific class of metallocene complexes in combination with a cocatalyst system comprising a boron containing cocatalyst and an aluminoxane cocatalyst, preferably in a multistage polymerization process including a gas phase polymerization step.