diff --git a/src/Avalonia.Controls/Window.cs b/src/Avalonia.Controls/Window.cs
index b21f18a59d..ee596432f7 100644
--- a/src/Avalonia.Controls/Window.cs
+++ b/src/Avalonia.Controls/Window.cs
@@ -570,8 +570,8 @@ namespace Avalonia.Controls
         protected override Size MeasureOverride(Size availableSize)
         {
             var sizeToContent = SizeToContent;
-            var constraint = availableSize;
             var clientSize = ClientSize;
+            var constraint = clientSize;
 
             if (sizeToContent.HasFlagCustom(SizeToContent.Width))
             {