A push-pull chain actuator (1) includes a housing with a chain exit/entry opening (4) and a sprocket (9) arranged to engage a push-pull chain (3). The sprocket (9) causes the polygon effect. The actuator includes a first chain guide part (10a) for guiding said push-pull chain (3) around the sprocket (9) and a second chain guide part (lob) for guiding said push-pull chain (3) at the correct angle between the chain exit/entry opening (4) and the sprocket (9). The second chain guide part (10b) is shaped and dimensioned to counteract the polygon effect. Alternatively, the second chain guide part (10b) can be shaped and dimensioned to reduce chain oscillations caused by the rollers (8c) engaging or disengaging the chain exit/entry opening (4) at the end of the second chain guide part (10b).