diff --git a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
index 8552f8d884cbc..1e9f20c294311 100644
--- a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
+++ b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
@@ -650,6 +650,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\CompilerServices\IntrinsicAttribute.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\CompilerServices\IsByRefLikeAttribute.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\CompilerServices\IsConst.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\CompilerServices\IsExternalInit.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\CompilerServices\IsReadOnlyAttribute.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\CompilerServices\IsVolatile.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\CompilerServices\IteratorStateMachineAttribute.cs" />
diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/IsExternalInit.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/IsExternalInit.cs
new file mode 100644
index 0000000000000..1581e78c36fec
--- /dev/null
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/IsExternalInit.cs
@@ -0,0 +1,17 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.ComponentModel;
+
+namespace System.Runtime.CompilerServices
+{
+    /// <summary>
+    /// Reserved to be used by the compiler for tracking metadata.
+    /// This class should not be used by developers in source code.
+    /// </summary>
+    [EditorBrowsable(EditorBrowsableState.Never)]
+    public static class IsExternalInit
+    {
+    }
+}
diff --git a/src/libraries/System.Runtime/ref/System.Runtime.cs b/src/libraries/System.Runtime/ref/System.Runtime.cs
index b01e3a2072ad8..f3180254cc80e 100644
--- a/src/libraries/System.Runtime/ref/System.Runtime.cs
+++ b/src/libraries/System.Runtime/ref/System.Runtime.cs
@@ -9097,6 +9097,10 @@ public IsByRefLikeAttribute() { }
     public static partial class IsConst
     {
     }
+    [System.ComponentModel.EditorBrowsableAttribute(System.ComponentModel.EditorBrowsableState.Never)]
+    public static partial class IsExternalInit
+    {
+    }
     [System.AttributeUsageAttribute(System.AttributeTargets.All, Inherited=false)]
     [System.ComponentModel.EditorBrowsableAttribute(System.ComponentModel.EditorBrowsableState.Never)]
     public sealed partial class IsReadOnlyAttribute : System.Attribute