How do I correct my far-too-sensitive proximity sensor?

I have a Samsung Galaxy Nexus (GSM). The sensor that turns the screen off in my pocket or at my cheek is suddenly turning the screen off when my thumb is within two inches of the top of the screen. It is difficult to grab the notification bar without triggering it, and holding my phone sideways is now an exercise in frustration. Is there a way to fix this? Did some update recently come out for this device?