'Loose' focussing ring

I have a 50mm 1.7 lens with a loose focussing ring. It focusses fine but at each extremes of focus the ring continues to turn. Any idea if I can fix this?

Thanks

I doubt you can fix it yourself, I had a similar problem with a 35-135 F lens. The inner drum (part of the lens that projects out of the barrel as you focus) could be removed completely and was at risk of falling out.
I had no option but to send it for repair.
Assuming your lens is reasonably secure and focussing nicely, you could just live with it or look for a replacement.
The 50mm 1.7 is a superb lens but the repair cost would most likely be much more than a second-hand replacement.