Roller shutter for shutting off an opening, comprising: - a curtain which is formed by longitudinal slats articulated laterally to one another along their longitudinal edges, is able to be moved substantially parallel to the opening and comprises a longitudinal end slat (L') generally forming the free lower edge of the curtain, - a protective casing which is able to contain the curtain and comprises a longitudinal passage slot configured to successively let through the said longitudinal slats during the movement of the curtain, the casing generally forming the upper edge of the opening, - a winding shaft housed in the protective casing and around which the curtain can be wound, - driving means for rotationally driving the winding shaft so as to manoeuvre the curtain between a wound position in which it is wound around the winding shaft and in which the end slat (L') of the curtain is in the vicinity of the longitudinal passage slot, along the upper edge of the opening, and a deployed position in which the curtain shuts off the opening and in which the end slat (L') of the curtain is on the opposite side from the protective casing in the opening, along the lower edge of the opening, - the end slat (L') and the longitudinal passage slot of the protective casing are configured in such a way that the end slat (L') shuts off the longitudinal passage slot of the protective casing when the curtain is in the wound position, - the end slat (L') is in one piece, and - the end slat (L') comprises a shut-off portion of which the thickness is greater than the width of the longitudinal passage slot and of which two opposite faces (F1, F2) butt against the respective lips (3a, 3b) of the longitudinal passage slot when the curtain is in the wound position, characterised in that: - the shut-off portion comprises two transverse shut-off facets (5c, 5d) which are respectively arranged on the one and the other of the opposite faces (F1, F2) of the end slat (L') and which bear against the lips (3a, 3b) of the longitudinal passage slot when the curtain is in the wound position, - the transverse shut-off facets (5c, 5d) are substantially coplanar and perpendicular to the mid-plane (A-A) of the curtain. - a curtain which is formed by longitudinal slats articulated laterally to one another along their longitudinal edges, is able to be moved substantially parallel to the opening and comprises a longitudinal end slat (L') generally forming the free lower edge of the curtain, - a protective casing which is able to contain the curtain and comprises a longitudinal passage slot configured to successively let through the said longitudinal slats during the movement of the curtain, the casing generally forming the upper edge of the opening, - a winding shaft housed in the protective casing and around which the curtain can be wound, - driving means for rotationally driving the winding shaft so as to manoeuvre the curtain between a wound position in which it is wound around the winding shaft and in which the end slat (L') of the curtain is in the vicinity of the longitudinal passage slot, along the upper edge of the opening, and a deployed position in which the curtain shuts off the opening and in which the end slat (L') of the curtain is on the opposite side from the protective casing in the opening, along the lower edge of the opening, - the end slat (L') and the longitudinal passage slot of the protective casing are configured in such a way that the end slat (L') shuts off the longitudinal passage slot of the protective casing when the curtain is in the wound position, - the end slat (L') is in one piece, and - the end slat (L') comprises a shut-off portion of which the thickness is greater than the width of the longitudinal passage slot and of which two opposite faces (F1, F2) butt against the respective lips (3a, 3b) of the longitudinal passage slot when the curtain is in the wound position, - the shut-off portion comprises two transverse shut-off facets (5c, 5d) which are respectively arranged on the one and the other of the opposite faces (F1, F2) of the end slat (L') and which bear against the lips (3a, 3b) of the longitudinal passage slot when the curtain is in the wound position, - the transverse shut-off facets (5c, 5d) are substantially coplanar and perpendicular to the mid-plane (A-A) of the curtain.