Cheap folding bike - wobbly handlebar - suggestions?

alx400
alx400 Posts: 13
edited July 2011 in The workshop
I've just received the Oyama folding bike I picked up cheaply online. it's obviously no Brompton but the bike actually looks better than I was expecting for the money. However there's a slight wobble to the handlebars.

They're the t-shaped type that slide down into the steerer(?) tube and get secured by a quick release. There's a plastic shim in there but I think it's a bit loose/mishapen. Can I just add some extra shim to hold it in place or is something else missing that should secure it?

Cheers,
Alex