A tappet (1), either for a high-pressure fuel pump or for a valve train of an internal combustion engine, with a housing (2) whose driven side (3) used for a contact of a tappet-following part forms a contact on a bottom side (4) of a bridge part (6) projecting through an inner casing (5) of the housing (2). An anti-rotation locking device (10) projects past the outer casing (8) of the housing with a first cylinder section (9) and sits in a window (7) of the housing (2), with this anti-rotation locking device (10) being provided as a cylindrical element, and tab-like projections (13) project from peripheral walls (11) of the window (7) and the anti-rotation locking device (10), standing “loose” in the window (7), snaps behind these projections. A second cylinder section (14) of the anti-rotation locking device extends behind the inner casing (5) of the housing (2), and the bridge part (6), extending on an axial section of the anti-rotation locking device (10), has in its peripheral section a recess (15) in its outer surface (16), with the second cylinder section (14) of the anti-rotation locking device (10) being supported against this recess.