diff --git "a/sdk/include/ddk/portcls.h" "b/sdk/include/ddk/portcls.h"
index 1c88b2401b..9f414377e3 100644
--- "a/sdk/include/ddk/portcls.h"
+++ "b/sdk/include/ddk/portcls.h"
@@ -2223,6 +2223,21 @@ DEFINE_GUID(IID_IMusicTechnology,
     IPreFetchOffset Interface
 */
 
+DECLARE_INTERFACE_(IPreFetchOffset,IUnknown) 
+{ 
+    DEFINE_ABSTRACT_UNKNOWN()   //  For IUnknown
+ 
+    STDMETHOD_(VOID,SetPreFetchOffset) 
+    (   THIS_ 
+        __in  ULONG   PreFetchOffset 
+    )   PURE; 
+}; 
+
+typedef IPreFetchOffset *PPREFETCHOFFSET;
+
+DEFINE_GUID(IID_IPreFetchOffset, 
+0x7000f480L, 0xed44, 0x4e8b, 0xb3, 0x8a, 0x41, 0x2f, 0x8d, 0x7a, 0x50, 0x4d); 
+
 /* ===============================================================
     PortCls API Functions
 */