An apparatus for use in erecting a temporary guardrail on a stair, having a stair stringer. The apparatus has an elongated stanchion. A first jaw assembly is operatively attached to the stanchion for engaging one side of the stringer, proximal the bottom edge thereof, and includes a first compression assembly to operatively urge the stanchion against the stringer. A second axially spaced, jaw assembly is operatively attached to the stanchion for engaging the one side of the stringer proximal a top edge thereof, and includes a second compression assembly to urge the stanchion against the stringer, and a bracket attached to the stanchion, and being adapted to receive a temporary guardrail member.