A ribbon cartridge construction and method of assembling same includes providing a housing with a ribbon access window at the outer perimeter thereof between ribbon inlet and outlet apertures for exposing a run of ribbon for use in printing on an oppositely facing surface and shielding all but a predetermined portion of the exposed ribbon from an oppositely facing surface. The shielding comprises providing a resiliently flexible planar shield including a shielding portion configured to cover the exposed ribbon and having a printing aperture corresponding in size to said predetermined portion of the exposed ribbon and two elongated mounting arms extending outwardly from the shielding portion in opposite directions. One arm is slid longitudinally into one ribbon aperture until fully inserted and is thereby automatically locked in to prevent removal and the other arm is slid longitudinally into the other ribbon aperture to put the shield in its operative position wherein the printing aperture is aligned with the predetermined portion of the ribbon.