The present invention relates to a smoke or fire barrier for closing an opening in a building, the barrier including: a curtain for closing the opening; means arrangeable at a head of the opening for deploying the curtain and for retracting the curtain; guide means at sides of the opening for retaining edges of the curtain after deployment and for reducing flow of smoke past the edges of the curtain, the guide means including: a pair of jaws for holding the edges of the deployed curtain, at least one of the jaws being movable towards the other and means for moving the or each movable jaw after deployment of the curtain.