A pre-manufactured door buck or a kit of parts is used to install a pre-sized door buck in a wall that allows a standard sized door to be installed. The door buck can include a pair of side members and a header member. Each side member can have an aperture passing through the side member. The header member can have a first end with a first tenon and a second end with a second tenon. The door buck is constructed by inserting the first tenon and the second tenon through the apertures in the side members and secured in place. The assembled door buck defines a pre-determined sized opening in which a door can be installed.