diff --git a/include/windows.storage.streams.idl b/include/windows.storage.streams.idl
index 8e8aba3b377..cc58a037f13 100644
--- a/include/windows.storage.streams.idl
+++ b/include/windows.storage.streams.idl
@@ -38,6 +38,7 @@ namespace Windows.Storage.Streams {
     interface IRandomAccessStreamStatics;
     interface IRandomAccessStreamWithContentType;
     runtimeclass Buffer;
+    runtimeclass InMemoryRandomAccessStream;
     runtimeclass RandomAccessStream;
     runtimeclass RandomAccessStreamReference;
 
@@ -129,6 +130,19 @@ namespace Windows.Storage.Streams {
     {
     }
 
+    [
+        activatable(Windows.Foundation.UniversalApiContract, 1.0),
+        contract(Windows.Foundation.UniversalApiContract, 1.0),
+        marshaling_behavior(agile)
+    ]
+    runtimeclass InMemoryRandomAccessStream
+    {
+        [default] interface Windows.Storage.Streams.IRandomAccessStream;
+        interface Windows.Storage.Streams.IOutputStream;
+        interface Windows.Foundation.IClosable;
+        interface Windows.Storage.Streams.IInputStream;
+    }
+
     [
         activatable(Windows.Storage.Streams.IBufferFactory, Windows.Foundation.UniversalApiContract, 1.0),
         contract(Windows.Foundation.UniversalApiContract, 1.0),