Abstract. Ice-shelf buttressing and the stability of marine-type ice sheets is investigated numerically. Buttressing effects are analysed for a situation where a stable grounding line is located on a bed sloping upwards in the direction of flow. Such grounding-line positions are known to be unconditionally unstable in the absence of transverse flow variations. It is shown that ice-shelf buttressing effects are responsible for restoring stability. Ice flux at the grounding line is, in general, not a monotonically increasing function of ice thickness. This, at first sight possibly somewhat counterintuitive result, is found to be fully consistent with recent theoretical work.