diff --git a/src/Microsoft.DotNet.Wpf/src/WindowsBase/System/Windows/Media/Matrix.cs b/src/Microsoft.DotNet.Wpf/src/WindowsBase/System/Windows/Media/Matrix.cs
index a95e23c2fd3..4fddb34835b 100644
--- a/src/Microsoft.DotNet.Wpf/src/WindowsBase/System/Windows/Media/Matrix.cs
+++ b/src/Microsoft.DotNet.Wpf/src/WindowsBase/System/Windows/Media/Matrix.cs
@@ -45,7 +45,7 @@ public partial struct Matrix: IFormattable
     {
         // the transform is identity by default
         // Actually fill in the fields - some (internal) code uses the fields directly for perf.
-        private static Matrix s_identity = CreateIdentity();
+        private static readonly Matrix s_identity = CreateIdentity();
 
 #region Constructor