Abstract: A fixed-nib writing instrument having a shaft extending along a longitudinal axis (A) and at the front of which a protective sleeve is mounted such that it can move coaxially with respect to the shaft, the sleeve moving between a protecting position in which it covers the writing nib and a retracted position in which it enables writing, the sleeve having a wall section which includes at least one helical guide path in engagement with at least one peg connected to the shaft in order that a rotation of the sleeve causes the latter to slide translationally between the protecting position and the retracted position.