The invention concerns a hydraulic piston machine, in particular a water hydraulic machine, with at least one cylinder, in which a piston (4) is arranged to reciprocate, the piston (4) comprising a hollow that is surrounded by an annular wall and has one open end. It is endeavored to keep cavitations small. For this purpose, a filling member (13) is arranged in the hollow (12), the filling member (13) having at least a radial projection (22) and the annular wall (16) having at least a radial depression (17) in the inside facing the hollow (12), or the annular wall (16) having a radial projection and the filing member (13) having a radial depression, the depression having a restraint (19), at least at the end adjacent to the open end (18) of the hollow (12), and the projection (22) and the depression (17) engaging each other.