A process for the preparation of a polypropylene in a sequential polymerization process including at least two polymerization reactors connected in series. The polymerization takes place in the presence of a Ziegler-Natta catalyst, and said Ziegler-Natta catalyst includes (a) a pro-catalyst that has a compound of a transition metal, a compound of a metal which metal is selected from one of the groups 1 to 3 of the periodic table (IUPAC), and an internal electron donor, (b) a co-catalyst, and (c) an external donor. The ratio of catalyst feed rate to propylene feed rate in the first polymerization reactor is 1.0 to 4.5 g/t.