A method for fixing rotary pistons in a rotary piston pump and a method for dismantling rotary pistons of a rotary piston pump, where the rotary piston pump has two counter-rotating rotary arranged in a pump space on drive shafts. The rotary pistons each include a seating for the drive shafts. The respective drive shaft is arranged and fixed with an end region in the seating of the respective rotary piston. A diameter of the drive shafts in the end region can be widened elastically. In an operational state, in which the rotary pistons are arranged on the respective drive shafts, a frictional connection is formed between the respective seating of the rotary piston and the end region of the respective drive shaft.