Iphone 6 plus compass error

My iPhone 6 plus compass has an error of approximately 40º off true. I have checked this with several calibrated marine compasses and other smartphone compasses. Is there any way to correct this error? It's extremely inconvenient as I need to carry two phones in order to navigate correctly using GPS. And no, I am NOT upgrading to iOS 9. My friend did and since then his phone has been nothing but problems. He won't even use his iPhone anymore.