A two-stroke crosshead engine with uniflow scavenging has a coke scraping ring in a cylinder and a piston (18) longitudinally displaceable in the cylinder and provided with piston rings (19, 19') which slide along the substantially cylindrical inner surface of the cylinder at the displacement of the piston and create a pressure-sealing separation between the volume below the piston and the working chamber (20), which is located above the uppermost piston ring of the piston and is defined by the uppermost piston ring (19'), the piston (18), the inner surface of the cylinder and the cylinder cover (8). The coke scraping ring (23) protrudes from the inner surface of the cylinder and extends annularly along it in an axial position so that the uppermost piston ring is positioned near the lower edge of the coke scraping ring when the piston is in its top dead centre position. In its cylindrical inner surface the coke scraping ring (23) is provided with several leakage grooves (24) which extend obliquely relative to the longitudinal axis of the cylinder from the lower surface to the top surface of the coke scraping ring. Alternatively, the leakage grooves may be provided in the cylindrical outer surface of the uppermost piston section (21) positioned above the uppermost piston ring.