A rotary piston engine in which the housing has an opening in at least one end wall that is controlled by the piston. The end seals on the piston and the sealing bolts at the juncture thereof are located radially inwardly from the opening, while the corner seals of the piston have legs at the ends of the piston extending to the sealing bolts. The corner seals are disposed in planes which in the radially inward direction diverge from the radial planes of the piston passing through the corners of the piston.