A protective apparatus for preventing the infiltration of contaminants in a fluid-operated percussion device, having a striking tool (3) that is guided to move in a housing (2) and is driven by a percussion piston in the striking direction (arrow 1), and a seal (7) that is supported at least indirectly on the housing (2), on the one hand, and on the striking tool (3), on the other hand, and has a securing segment that is fixedly disposed with respect to either the housing or the striking tool. The seal (7) is disposed between the inner guide portion (5b) of the striking-tool guide and the theoretical striking plane (4) of the percussive piston on the striking tool (3), when seen in the direction opposite the striking direction (arrow 1), such that the countersurface (3e) for the seal, which countersurface moves relative to the securing segment (7a) of the seal (7) and is in contact with the seal, is unaffected by wear.