diff --git a/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/CodeCompletion/CompletionWindowBase.cs b/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/CodeCompletion/CompletionWindowBase.cs
index 126144807f..bd2eed2f8f 100644
--- a/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/CodeCompletion/CompletionWindowBase.cs
+++ b/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/CodeCompletion/CompletionWindowBase.cs
@@ -244,10 +244,12 @@ namespace ICSharpCode.AvalonEdit.CodeCompletion
 		void UpdatePosition()
 		{
 			TextView textView = this.TextArea.TextView;
+			// PointToScreen returns device dependent units (physical pixels)
 			Point location = textView.PointToScreen(visualLocation - textView.ScrollOffset);
 			Point locationTop = textView.PointToScreen(visualLocationTop - textView.ScrollOffset);
 			
-			Size completionWindowSize = new Size(this.ActualWidth, this.ActualHeight);
+			// Let's use device dependent units for everything
+			Size completionWindowSize = new Size(this.ActualWidth, this.ActualHeight).TransformToDevice(this);
 			Rect bounds = new Rect(location, completionWindowSize);
 			Rect workingScreen = System.Windows.Forms.Screen.GetWorkingArea(location.ToSystemDrawing()).ToWpf();
 			if (!workingScreen.Contains(bounds)) {
@@ -263,6 +265,8 @@ namespace ICSharpCode.AvalonEdit.CodeCompletion
 					bounds.Y = workingScreen.Top;
 				}
 			}
+			// Convert the window bounds to device independent units
+			bounds = bounds.TransformFromDevice(this);
 			this.Left = bounds.X;
 			this.Top = bounds.Y;
 		}
diff --git a/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Utils/ExtensionMethods.cs b/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Utils/ExtensionMethods.cs
index c1db21e651..7a4d6519d8 100644
--- a/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Utils/ExtensionMethods.cs
+++ b/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Utils/ExtensionMethods.cs
@@ -161,6 +161,32 @@ namespace ICSharpCode.AvalonEdit.Utils
 		}
 		#endregion
 		
+		#region DPI independence
+		public static Rect TransformToDevice(this Rect rect, Visual visual)
+		{
+			Matrix matrix = PresentationSource.FromVisual(visual).CompositionTarget.TransformToDevice;
+			return Rect.Transform(rect, matrix);
+		}
+		
+		public static Rect TransformFromDevice(this Rect rect, Visual visual)
+		{
+			Matrix matrix = PresentationSource.FromVisual(visual).CompositionTarget.TransformFromDevice;
+			return Rect.Transform(rect, matrix);
+		}
+		
+		public static Size TransformToDevice(this Size size, Visual visual)
+		{
+			Matrix matrix = PresentationSource.FromVisual(visual).CompositionTarget.TransformToDevice;
+			return new Size(size.Width * matrix.M11, size.Height * matrix.M22);
+		}
+		
+		public static Size TransformFromDevice(this Size size, Visual visual)
+		{
+			Matrix matrix = PresentationSource.FromVisual(visual).CompositionTarget.TransformFromDevice;
+			return new Size(size.Width * matrix.M11, size.Height * matrix.M22);
+		}
+		#endregion
+		
 		#region System.Drawing <-> WPF conversions
 		public static System.Drawing.Point ToSystemDrawing(this Point p)
 		{