System.Net.Http.Formatting PCL assembly

I am using the ObjectContent class in the above assembly and it is causing an exception when the assembly is loaded.

System.TypeLoadException: Could not load type 'System.Net.Http.ObjectContent`1[MyProject.Client.Proxy.UserManagement+AuthenticationParameter]' from assembly 'System.Net.Http.Formatting, Version=5.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35'.

My PCL assembly project MyProject is targetting .Net Framework 4.5 and higher, WP8, Xamarin.Android and Xamarin.iOS. I'm running on VS2013.