A door frame system including a spline. Each door frame section includes a brickmould and a jamb each having a groove on at least one side and the door frame sections are joined together by the spline. The spline includes a polymeric material having a shape such so as to form a moisture-resistant seal along the length of the joint. The spline is concealed from view when the brickmould and a jamb are connected together to form a frame including a uniform reveal.