The invention is directed to a cover (4) for a tap of a gas cylinder (6), comprising a shell (7, 8) for housing the tap; and a hook (12) pivotally mounted on the shell (8), configured for securing the gas cylinder (6) to a horizontal bar (28). The shell (8) comprises reservations (30) on its external surface configured for receiving the hook (12) in a folded position so as to generally conform to said external surface. The invention is also directed to a gas storage assembly comprising a gas cylinder (6), a tap and a cover (4).