diff --git a/tests/Avalonia.UnitTests/TestRoot.cs b/tests/Avalonia.UnitTests/TestRoot.cs
index fe59a7851d..4a651d8fe7 100644
--- a/tests/Avalonia.UnitTests/TestRoot.cs
+++ b/tests/Avalonia.UnitTests/TestRoot.cs
@@ -42,7 +42,7 @@ namespace Avalonia.UnitTests
 
         public int NameScopeUnregisteredSubscribers { get; private set; }
 
-        public Size ClientSize => new Size(100, 100);
+        public Size ClientSize { get; set; } = new Size(100, 100);
 
         public Size MaxClientSize => Size.Infinity;