Check the screws, make sure they're tight (I almost lost mine after my first ride). I would suggest putting a small drop of LocTite on each screw. If the mount still swivels after tighten up the bolts, you might need to shim out the clamping area. You can small piece of inner tube or tape wrapped around the clamping area (I have done this in the past for bike computers, brake levers and etc that would't hold on tight enough).