Proximity sensor on IPhone 5 and IOS7 not working

Since the update to IOS7 on my IPhone 5 I sometimes switched the speaker on during a running phone call with my ears. To avoid this you should do the follwing after update your device to IOS 7:

1. Go to Settings->General->Reset->Reset All Settings
2. Reboot your device

thats it. A simple test can be done by calling your voice mail an during the call just put your finger on the sensor (it's located  left beside the camera on IPhone5). The sensor will turn of the display once you finger approaches the sensor.