This invention relates to a post holder (200) for holding a safety post on a horizontal structure of a building. The post holder has an elongate post reception portion (202), an elongate central support portion (204), protruding from the post reception portion and perpendicular to the post reception portion, and first and second elongate side support portions (206,208) protruding from the post reception portion laterally of the central support portion and in opposite directions. The central support portion comprises a fastening seat, which is arranged to receive a fastening member for fastening of the post holder to a base.