Abstract: The invention discloses a lid (1) for a compartment (101) in the frame (100) of a bicycle. The lid (1) comprises: two tracks (4) provided on an inner face (2i) of a plate (2) in an elevated position with respect to said inner face (2i) and finishing in respective drops (4e) towards respective lengths (2t) of a perimetral band (2p) of the inner face (2i) located at opposite sides of said plate (2); and a rotating body (6) provided on the inner face (2i) and comprising two arms (6b) continuously biased towards the inner face (2i). When the body (6) is rotated by actuating the actuator (3), the ends of the arms (6b) follow the tracks (4) until arriving at a fastening position where they fall down the drops (4e) towards the respective lengths (2t) of the perimetral band (2p), thereby fastening the lid (1) in the closed position.