diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/ArrayWithOffset.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/ArrayWithOffset.cs
index 5c4c319d883aca..fa0f9c0b28ced9 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/ArrayWithOffset.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/ArrayWithOffset.cs
@@ -6,7 +6,7 @@
 
 namespace System.Runtime.InteropServices
 {
-    public struct ArrayWithOffset
+    public readonly struct ArrayWithOffset
     {
         private readonly object? m_array;
         private readonly int m_offset;
diff --git a/src/libraries/System.Runtime.InteropServices/ref/System.Runtime.InteropServices.cs b/src/libraries/System.Runtime.InteropServices/ref/System.Runtime.InteropServices.cs
index 5fcb17353156e9..c9b9178c33b3b6 100644
--- a/src/libraries/System.Runtime.InteropServices/ref/System.Runtime.InteropServices.cs
+++ b/src/libraries/System.Runtime.InteropServices/ref/System.Runtime.InteropServices.cs
@@ -98,10 +98,10 @@ public sealed partial class AllowReversePInvokeCallsAttribute : System.Attribute
     {
         public AllowReversePInvokeCallsAttribute() { }
     }
-    public partial struct ArrayWithOffset
+    public readonly partial struct ArrayWithOffset
     {
-        private object _dummy;
-        private int _dummyPrimitive;
+        private readonly object _dummy;
+        private readonly int _dummyPrimitive;
         public ArrayWithOffset(object? array, int offset) { throw null; }
         public override bool Equals([System.Diagnostics.CodeAnalysis.NotNullWhenAttribute(true)] object? obj) { throw null; }
         public bool Equals(System.Runtime.InteropServices.ArrayWithOffset obj) { throw null; }