Cannot get view to use entire screen width on iPhone 6+

In my storyboard I have a MapView that I would like to use the entire width of the screen. I created two constraints for the leading and the trailing space and they are set up as follows:

On the iPhone 4S - 6 the view works as expected, with the map using the entire screen width. But on the 6+ I can see that the map isn't using the entire width and has about 5px of padding on both sides, as seen here - it's hard to see with the background being white:

How can I make this mapview use the entire width of the screen for the 6+?