diff --git a/src/Avalonia.Controls/DefinitionBase.cs b/src/Avalonia.Controls/DefinitionBase.cs
index 8c069b6786..56e2cab298 100644
--- a/src/Avalonia.Controls/DefinitionBase.cs
+++ b/src/Avalonia.Controls/DefinitionBase.cs
@@ -3,18 +3,15 @@
 // 
 // Licensed to The Avalonia Project under MIT License, courtesy of The .NET Foundation.
 
-using MS.Internal;
-using MS.Internal.KnownBoxes;
 using System;
 using System.Collections;
 using System.Collections.Generic;
-using System.ComponentModel;
 using System.Diagnostics;
-using System.Security.Permissions;
-using System.Windows;
-using System.Windows.Threading;
 
-namespace System.Windows.Controls
+using Avalonia;
+using Avalonia.Collections;
+
+namespace Avalonia.Controls
 {
     /// <summary>
     /// DefinitionBase provides core functionality used internally by Grid