A knee airbag having a first wall extending from an upper end and having a first outer surface serving as an impact surface being positioned opposite the knee-shin-area of an occupant to be protected when the airbag is fully deployed, and a second wall extending from a rear end adjacent or identical to the upper end of the first wall and having a second outer surface. The second wall comprises a first section, a second section and a groove section being positioned between the first section and the second section such that the second outer surface shows a groove. In order to make the knee airbag suitable for a vehicle that does not provide sufficient instrument panel surface to support it, the first wall and the first and second sections of the second wall enclose an angle between 20° and 80°, preferably between 30° and 60°.