An injection device (1) for delivering a predetermined fixed dose of liquid drug, the device (1) comprising a housing (2), a first and second tubular members (7, 10). The first tubular member (7) and the housing are engaged via a first track (8) and a first protruding part (9), and the first and second tubular members (7, 10) are engaged via a second track (11) and a second protruding part (12). The first track (8) comprises a first portion (8a) which the first protruding part (9) travels during setting of the dose, and the second track (11) comprises a first portion (11a) which the second protruding part (12) travels during setting of the predetermined fixed dose. The first 10 portions (8a, 11a) of the first (8) and second (11) tracks are shaped in such a manner that the second tubular member (10) is prevented from rotating during setting 15 of a dose. The second tubular member (10) is rotationally locked to a piston rod (13), and rotation of the piston rod (13) during dose setting is thereby prevented.
