Apparatus for stabilizing the deployment of an airbag includes an airbag housing in which a folded up airbag is housed. The housing has an open side through which the airbag is deployed and a door is pivoted to the housing and is pivoted open by the deploying airbag. An extension panel is mounted on the door by a track mechanism so that the extension panel is movable between a normal retracted position along side the door and an extended position in which the extension panel extends beyond the door. An extension mechanism for causes the extension panel to be moved to the extended position when the airbag is deploying so that the door and the extension panel direct and stabilize the deploying airbag.