diff --git a/src/Avalonia.Controls/Window.cs b/src/Avalonia.Controls/Window.cs
index 505f3f7416..feacc3e63a 100644
--- a/src/Avalonia.Controls/Window.cs
+++ b/src/Avalonia.Controls/Window.cs
@@ -879,7 +879,7 @@ namespace Avalonia.Controls
 
             if (startupLocation == WindowStartupLocation.CenterScreen)
             {
-                Screen screen = null;
+                Screen? screen = null;
 
                 if (owner is not null)
                 {