diff --git a/src/libraries/System.Runtime.CompilerServices.VisualC/ref/System.Runtime.CompilerServices.VisualC.cs b/src/libraries/System.Runtime.CompilerServices.VisualC/ref/System.Runtime.CompilerServices.VisualC.cs
index 7600470f413db..1d5079f52cdf1 100644
--- a/src/libraries/System.Runtime.CompilerServices.VisualC/ref/System.Runtime.CompilerServices.VisualC.cs
+++ b/src/libraries/System.Runtime.CompilerServices.VisualC/ref/System.Runtime.CompilerServices.VisualC.cs
@@ -66,6 +66,11 @@ public sealed partial class NativeCppClassAttribute : System.Attribute
     {
         public NativeCppClassAttribute() { }
     }
+    [AttributeUsage(AttributeTargets.Assembly, AllowMultiple=true)]
+    public sealed class CppInlineNamespaceAttribute : Attribute
+    {
+        public CppInlineNamespaceAttribute(string dottedName) {}
+    }
     [System.AttributeUsageAttribute(System.AttributeTargets.Class | System.AttributeTargets.Enum | System.AttributeTargets.Interface | System.AttributeTargets.Struct, AllowMultiple=true, Inherited=false)]
     public sealed partial class RequiredAttributeAttribute : System.Attribute
     {
diff --git a/src/libraries/System.Runtime.CompilerServices.VisualC/src/System/Runtime/CompilerServices/Attributes.cs b/src/libraries/System.Runtime.CompilerServices.VisualC/src/System/Runtime/CompilerServices/Attributes.cs
index ec989201762df..18dad6f87f40b 100644
--- a/src/libraries/System.Runtime.CompilerServices.VisualC/src/System/Runtime/CompilerServices/Attributes.cs
+++ b/src/libraries/System.Runtime.CompilerServices.VisualC/src/System/Runtime/CompilerServices/Attributes.cs
@@ -121,6 +121,12 @@ public sealed class NativeCppClassAttribute : Attribute
         public NativeCppClassAttribute() { }
     }
 
+    [AttributeUsage(AttributeTargets.Assembly, AllowMultiple=true)]
+    public sealed class CppInlineNamespaceAttribute : Attribute
+    {
+        public CppInlineNamespaceAttribute(string dottedName) {}
+    }
+
     [AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Enum | AttributeTargets.Interface, AllowMultiple = true, Inherited = false)]
     public sealed class RequiredAttributeAttribute : Attribute
     {