diff --git a/include/guiddef.h b/include/guiddef.h
index d0a6265..4d1c36f 100644
--- a/include/guiddef.h
+++ b/include/guiddef.h
@@ -52,16 +52,22 @@
 #endif /* ndef __IID_DEFINED__ */
 typedef GUID FMTID,*LPFMTID;
 
+#ifdef __midl_proxy
+#define __MIDL_CONST
+#else
+#define __MIDL_CONST const
+#endif
+
 #if defined(__cplusplus) && !defined(CINTERFACE)
 #define REFGUID             const GUID &
 #define REFCLSID            const CLSID &
 #define REFIID              const IID &
 #define REFFMTID            const FMTID &
 #else /* !defined(__cplusplus) && !defined(CINTERFACE) */
-#define REFGUID             const GUID* const
-#define REFCLSID            const CLSID* const
-#define REFIID              const IID* const
-#define REFFMTID            const FMTID* const
+#define REFGUID             const GUID* __MIDL_CONST
+#define REFCLSID            const CLSID* __MIDL_CONST
+#define REFIID              const IID* __MIDL_CONST
+#define REFFMTID            const FMTID* __MIDL_CONST
 #endif /* !defined(__cplusplus) && !defined(CINTERFACE) */
 
 #if defined(__cplusplus) && !defined(CINTERFACE)
diff --git a/include/rpcproxy.h b/include/rpcproxy.h
index 80e3c9e..cd88d1f 100644
--- a/include/rpcproxy.h
+++ b/include/rpcproxy.h
@@ -24,8 +24,12 @@
 #ifndef __WINE_RPCPROXY_H
 #define __WINE_RPCPROXY_H
 
+#define __midl_proxy
+
 #include <basetsd.h>
+#ifndef GUID_DEFINED
 #include <guiddef.h>
+#endif
 #include <rpc.h>
 #include <rpcndr.h>