diff --git a/EmulatorPkg/Library/ThunkProtocolList/ThunkProtocolList.c b/EmulatorPkg/Library/ThunkProtocolList/ThunkProtocolList.c
index b2daa2bef5..9fa9e25e94 100644
--- a/EmulatorPkg/Library/ThunkProtocolList/ThunkProtocolList.c
+++ b/EmulatorPkg/Library/ThunkProtocolList/ThunkProtocolList.c
@@ -2,7 +2,7 @@
   Emulator Thunk to abstract OS services from pure EFI code
 
   Copyright (c) 2008 - 2011, Apple Inc. All rights reserved.<BR>
-  Copyright (c) 2011, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2011 - 2018, Intel Corporation. All rights reserved.<BR>
 
   This program and the accompanying materials
   are licensed and made available under the terms and conditions of the BSD License
@@ -82,7 +82,7 @@ AddThunkProtocol (
     Private->EmuBusDriver       = EmuBusDriver;
 
     CopyMem (&Private->Data, ThunkIo, sizeof (EMU_IO_THUNK_PROTOCOL));
-    Private->Data.Instance      = Instance++;
+    Private->Data.Instance      = (UINT16)Instance++;
     Private->Data.ConfigString  = StartString;
 
     InsertTailList (&mThunkList, &Private->Link);