Glass fallen out of pivot shower door

[flynnr]

Hi,
The glass has fallen out of my pivot shower door twice, it hasn't broken (although it did chip the enamel of the bath and nearly kill me!). I put it back in once but it fell out again. There doesn't appear to be anything holding it in other than the fact that it was originally wedged in quite tightly. There are no holes in the glass for putting nuts through it etc. Does anyone know how I can get it to stay in, if I am doing something incorrectly?
Thanks!