How can I use EditorRenderer in a Unified API app?

I've converted a small project from Classic to Unified, but now I'm getting the following compile errors:

Error CS0012: The type MonoTouch.UIKit.UITextView' is defined in an assembly that is not referenced. Consider adding a reference to assemblymonotouch, Version=0.0.0.0, Culture=neutral, PublicKeyToken=84e04ff9cfb79065' (CS0012) (RTChex.Forms.iOS)

Error CS0012: The type MonoTouch.UIKit.UIView' is defined in an assembly that is not referenced. Consider adding a reference to assemblymonotouch, Version=0.0.0.0, Culture=neutral, PublicKeyToken=84e04ff9cfb79065' (CS0012) (RTChex.Forms.iOS)

Error CS0012: The type MonoTouch.UIKit.UITextField' is defined in an assembly that is not referenced. Consider adding a reference to assemblymonotouch, Version=0.0.0.0, Culture=neutral, PublicKeyToken=84e04ff9cfb79065' (CS0012) (RTChex.Forms.iOS)

Code is as follows:

using System;
using Xamarin.Forms.Platform.iOS;
using UIKit;
using Xamarin.Forms;

[assembly: ExportRenderer(typeof(ExtendedEditor), typeof(ExtendedEditorRenderer))]
namespace MyProject.Renderers
{
    public class ExtendedEditorRenderer : EditorRenderer
    {
    }
}

The error occurs on the reference to EditorRenderer as the base class for ExtendedEditorRenderer.

I searched a bit online but didn't find anything, perhaps I'm missing an obvious step? My project no longer references the monotouch project, but instead references Xamarin.Forms which is where UITextView should be defined. I'm on Xamarin Forms 1.3.4.