A method for modifying a multistage compressor (101) involves exchanging the rotor blades of the first compressor rotor blade row (LA1) for modified rotor blades which have an identical blade leaf profile (121) to the original rotor blades and the blade angle (B′11) of which is different from the blade angle (B′10) of the original rotor blades. Furthermore, the blades of at least one further blade row (LAN, LEN) arranged downstream of the second compressor stage are exchanged for modified blades which have an identical blade leaf profile (125, 126) to the original blades and the blade angle (B′N1, B″N1) of which is different from the blade angle (B′NO, B″NO) of the original blades. The method makes it possible to increase the mass flow of a compressor and essentially maintain the stability reserve against stall.