The invention relates to an internal gear pump for a braking system, in the pump housing of which an inner toothed hollow wheel and a gearwheel engaging in the toothing of the hollow wheel are mounted to rotate about parallel axes. The toothing thereof defines a tapering roughly crescent-shaped pump chamber, in which a filling piece is arranged supported along the length thereof. The circumferential surfaces of the filling piece closely correspond to the head diameter of the inner toothing of the hollow wheel or the gearwheel toothing and contact in a sealing manner with several tooth crowns covered thereby. A radial supporting force acts over a longitudinal range of the filling piece for improved sealing of a circumferential surface of the filling piece against the tooth crowns supporting the circumferential surface. According to the invention, a loose fit is provided between the circumferential surfaces of the filling piece and the opposing tooth crowns of the hollow wheel and gearwheel and the play acting on the filling piece is partly eliminated by support forces acting in opposing radial directions which act on the filling piece at a distance from each other.