A film damper for a gas turbine engine includes an annular inner member and an annular outer member located radially outboard of the annular inner member, the annular outer member and the annular inner member defining a damper annulus therebetween. A fluid supply passage delivers a flow of fluid into the damper annulus from the annular outer member, and a backflow prevention device is located at the fluid supply passage to prevent backflow of the flow of fluid from the damper annulus into the fluid supply passage.