Add another readonly attribute

diff --git a/src/System.Private.CoreLib/shared/System/Text/StringBuilder.cs b/src/System.Private.CoreLib/shared/System/Text/StringBuilder.cs
index e760283..964a56a 100644 (file)
--- a/src/System.Private.CoreLib/shared/System/Text/StringBuilder.cs
+++ b/src/System.Private.CoreLib/shared/System/Text/StringBuilder.cs
@@ -584,7 +584,7 @@ namespace System.Text
         /// It needs to be public (so the compiler can use it when building a foreach statement) 
         /// but users typically don't use it explicitly (which is why it is a nested type).  
         /// </summary>
-        public struct ChunkEnumerable
+        readonly public struct ChunkEnumerable
         {
             /// <summary>
             /// Implements the IEnumerable pattern.