A base for a child safety seat includes a shell body, a support leg and an abutment device. The shell body has a bottom surface and a lengthwise axis, the bottom surface being adapted to rest on an upper surface of a vehicle seat. The support leg is operable to extend downward from the bottom surface to provide a first abutment in a first direction against a floor of a vehicle. The abutment device is operable to extend below the bottom surface to provide a second abutment in a second direction against an upright surface of the vehicle, the upright surface being located above the floor and below the upper surface of the vehicle seat.