diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/RuntimeFeature.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/RuntimeFeature.cs
index a94a0e19d01761..9e0a5ed29e42e8 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/RuntimeFeature.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/RuntimeFeature.cs
@@ -27,6 +27,11 @@ public static partial class RuntimeFeature
         /// </summary>
         public const string CovariantReturnsOfClasses = nameof(CovariantReturnsOfClasses);
 
+        /// <summary>
+        /// Represents a runtime feature where types can define ref fields.
+        /// </summary>
+        public const string ByRefFields = nameof(ByRefFields);
+
         /// <summary>
         /// Indicates that this version of runtime supports virtual static members of interfaces.
         /// </summary>
@@ -42,6 +47,7 @@ public static bool IsSupported(string feature)
             {
                 case PortablePdb:
                 case CovariantReturnsOfClasses:
+                case ByRefFields:
                 case UnmanagedSignatureCallingConvention:
                 case DefaultImplementationsOfInterfaces:
 #pragma warning disable CA2252
diff --git a/src/libraries/System.Runtime/ref/System.Runtime.cs b/src/libraries/System.Runtime/ref/System.Runtime.cs
index c57c5b13cc1190..8006340a876657 100644
--- a/src/libraries/System.Runtime/ref/System.Runtime.cs
+++ b/src/libraries/System.Runtime/ref/System.Runtime.cs
@@ -13206,6 +13206,7 @@ public RuntimeCompatibilityAttribute() { }
     }
     public static partial class RuntimeFeature
     {
+        public const string ByRefFields = "ByRefFields";
         public const string CovariantReturnsOfClasses = "CovariantReturnsOfClasses";
         public const string DefaultImplementationsOfInterfaces = "DefaultImplementationsOfInterfaces";
         public const string PortablePdb = "PortablePdb";