A knee airbag having an inlet opening (6) for deployment gas from a gas generator (4) for flowing into a first chamber (10), at least one second chamber (20, 30) adjacent to the first chamber (10), which second chamber (20, 30) is separated from the first chamber by at least one dividing wall (25), wherein between the first chamber (10) and the second chamber (20, 30) at least one closable overflow opening (40) is provided, through which deployment gas can flow from the first chamber (10) into the second chamber (20, 30), wherein at least one closing device (50 for the overflow opening (40), or the overflow opening (40), is associated with the penetration region of the knees (5).