diff --git a/include/commctrl.h b/include/commctrl.h
index 05f16aace82..9f546b23fd0 100644
--- a/include/commctrl.h
+++ b/include/commctrl.h
@@ -12,21 +12,21 @@
 
 /* c++ likes nameless unions whereas c doesnt */
 /* (used in property sheet structures)        */
-#ifdef __cplusplus
+#if defined(__cplusplus) && !defined(NONAMELESSUNION)
 #define DUMMYUNIONNAME
 #define DUMMYUNIONNAME1
 #define DUMMYUNIONNAME2
 #define DUMMYUNIONNAME3
 #define DUMMYUNIONNAME4
 #define DUMMYUNIONNAME5
-#else
+#else /* defined(__cplusplus) && !defined(NONAMELESSUNION) */
 #define DUMMYUNIONNAME   u
 #define DUMMYUNIONNAME1  u1
 #define DUMMYUNIONNAME2  u2
 #define DUMMYUNIONNAME3  u3
 #define DUMMYUNIONNAME4  u4
 #define DUMMYUNIONNAME5  u5
-#endif
+#endif /* defined(__cplusplus) && !defined(NONAMELESSUNION) */
 
 #ifdef __cplusplus
 extern "C" {
diff --git a/include/prsht.h b/include/prsht.h
index f975124355f..8fa8822953e 100644
--- a/include/prsht.h
+++ b/include/prsht.h
@@ -31,21 +31,21 @@ typedef BOOL (CALLBACK *LPFNADDPROPSHEETPAGES)(LPVOID, LPFNADDPROPSHEETPAGE, LPA
 
 /* c++ likes nameless unions whereas c doesnt */
 /* (used in property sheet structures)        */
-#ifdef __cplusplus
+#if defined(__cplusplus) && !defined(NONAMELESSUNION)
 #define DUMMYUNIONNAME
 #define DUMMYUNIONNAME1
 #define DUMMYUNIONNAME2
 #define DUMMYUNIONNAME3
 #define DUMMYUNIONNAME4
 #define DUMMYUNIONNAME5
-#else
+#else /*  defined(__cplusplus) && !defined(NONAMELESSUNION) */
 #define DUMMYUNIONNAME   u
 #define DUMMYUNIONNAME1  u1
 #define DUMMYUNIONNAME2  u2
 #define DUMMYUNIONNAME3  u3
 #define DUMMYUNIONNAME4  u4
 #define DUMMYUNIONNAME5  u5
-#endif
+#endif /* defined(__cplusplus) && !defined(NONAMELESSUNION) */
 
 /*
  * Property sheet support (structures)
diff --git a/include/wine/obj_dataobject.h b/include/wine/obj_dataobject.h
index 8e6432c67e0..b6e98e5f7d0 100644
--- a/include/wine/obj_dataobject.h
+++ b/include/wine/obj_dataobject.h
@@ -7,11 +7,15 @@
 #ifndef __WINE_WINE_OBJ_DATAOBJECT_H
 #define __WINE_WINE_OBJ_DATAOBJECT_H
 
+#if defined(__cplusplus) && !defined(NONAMELESSUNION)
+#define DUMMYUNIONNAME
+#else /* defined(__cplusplus) && !defined(NONAMELESSUNION) */
+#define DUMMYUNIONNAME u
+#endif /* defined(__cplusplus) && !defined(NONAMELESSUNION) */
+
 #ifdef __cplusplus
-#define DUMMY_UNION_NAME
-#else
-#define DUMMY_UNION_NAME u
-#endif
+extern "C" {
+#endif /* defined(__cplusplus) */
 
 /*****************************************************************************
  * Predeclare the structures
@@ -118,7 +122,7 @@ struct STGMEDIUM
         LPOLESTR lpszFileName;
         IStream *pstm;
         IStorage *pstg;
-    } DUMMY_UNION_NAME;
+    } DUMMYUNIONNAME;
     IUnknown *pUnkForRelease;
 };   
 
diff --git a/include/wtypes.h b/include/wtypes.h
index 1ffa1159a4c..da6b5894cae 100644
--- a/include/wtypes.h
+++ b/include/wtypes.h
@@ -51,17 +51,17 @@ typedef GUID  *LPGUID;
 typedef GUID  CLSID,*LPCLSID;
 typedef GUID	IID,*LPIID;
 typedef GUID	FMTID,*LPFMTID;
-#ifdef __cplusplus
+#if defined(__cplusplus) && !defined(CINTERFACE)
 #define REFGUID             const GUID &
 #define REFCLSID            const CLSID &
 #define REFIID              const IID &
 #define REFFMTID            const FMTID &
-#else /* !defined(__cplusplus) */
+#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
-#endif /* !defined(__cplusplus) */
+#endif /* !defined(__cplusplus) && !defined(CINTERFACE) */
 
 extern const IID GUID_NULL;
 #define IID_NULL            GUID_NULL