Xam.Plugin.Geolocator Fail

Hello,

I'm using the Geolocator Plugin (https://github.com/jamesmontemagno/Xamarin.Plugins/tree/master/Geolocator). It works great on Android, but on iOS I get the following error on build:
"Failed to resolve "System.Void CoreLocation.CLLocationManager::set_AllowsBackgroundLocationUpdates(System.Boolean)" reference from "Xamarin.iOS, Version=0.0.0.0, Culture=neutral, PublicKeyToken=84e04ff9cfb79065"

What can I do?

Thanks
Xaver