An end cap for enclosing or covering the end of a cassette of a roller blind or a roller shade. The cassette includes a roller having wound thereon a fabric having a bottom bar attached or otherwise secured thereto or thereover. The end cap comprises a wall portion and a bottom bar stop. The wall portion is releasably securable to an end of the cassette. The bottom bar stop is fixed to and extends outwardly from the wall portion and inhibits upward movement of the bottom bar beyond the elevation of the bottom bar stop when the end cap is secured to an end of the cassette.