Assembly for arranging a temporary preceding guardrail on a scaffolding system comprising standards, ledgers and substantially tube-shaped guardrails (12, 14), the assembly comprising substantially tube-shaped guardrails (12, 14) and a preceding-guardrail holder configured for cooperation with the guardrails (12, 14) of the scaffolding system, wherein each guardrail of the assembly at a longitudinal end thereof is provided with a fastening hook which has a curvature around a curvature axis which is perpendicular to a longitudinal axis of the guardrail (12, 14), wherein the fastening hook on a radial inner side is provided with a recess, wherein the distance of the recess to a point on a radial outer side of the fastening hook gradually increases from a first point on the radial outer side to a second point on the radial outer side of the fastening hook, wherein the second point) is more remote from a center of the guardrail (12, 14) than the first point, wherein the preceding-guardrail holder is provided with a mounting plate and a retaining plate which extends substantially parallel to the mounting plate, wherein the mounting plate and the retaining plate are mutually connected by a first and a second cross connection element (38, 40) extending perpendicular to the mounting plate and retaining plate, wherein the two cross connection elements (38, 40) are mutually spaced apart and together bound a fastening hook receiving space for receiving in the fastening hook receiving space the fastening hook of a first of said guardrails (12, 14), wherein the distance between the first and the second cross connection element (38, 40) is such that, if the fastening hook is received in the fastening hook receiving space and the first guardrail is not supported otherwise, the recess on the radial inner side of the fastening hook rests on the first cross connection element and the radial outer side of the fastening hook abuts against the second cross connection element, the first guardrail thereby being wholly supported by the single preceding-guardrail holder. wherein each guardrail of the assembly at a longitudinal end thereof is provided with a fastening hook which has a curvature around a curvature axis which is perpendicular to a longitudinal axis of the guardrail (12, 14), wherein the fastening hook on a radial inner side is provided with a recess, wherein the distance of the recess to a point on a radial outer side of the fastening hook gradually increases from a first point on the radial outer side to a second point on the radial outer side of the fastening hook, wherein the second point) is more remote from a center of the guardrail (12, 14) than the first point, wherein the preceding-guardrail holder is provided with a mounting plate and a retaining plate which extends substantially parallel to the mounting plate, wherein the mounting plate and the retaining plate are mutually connected by a first and a second cross connection element (38, 40) extending perpendicular to the mounting plate and retaining plate, wherein the two cross connection elements (38, 40) are mutually spaced apart and together bound a fastening hook receiving space for receiving in the fastening hook receiving space the fastening hook of a first of said guardrails (12, 14), wherein the distance between the first and the second cross connection element (38, 40) is such that, if the fastening hook is received in the fastening hook receiving space and the first guardrail is not supported otherwise, the recess on the radial inner side of the fastening hook rests on the first cross connection element and the radial outer side of the fastening hook abuts against the second cross connection element, the first guardrail thereby being wholly supported by the single preceding-guardrail holder.