diff --git a/reactos/w32api/include/basetyps.h b/reactos/w32api/include/basetyps.h
index d8cb3c72cca..c4249cb2e79 100644
--- a/reactos/w32api/include/basetyps.h
+++ b/reactos/w32api/include/basetyps.h
@@ -113,6 +113,10 @@ typedef struct _GUID
     unsigned char Data4[8];
 } GUID,*REFGUID,*LPGUID;
 #endif /* GUID_DEFINED */
+#ifndef LPCGUID_DEFINED
+#define LPCGUID_DEFINED
+typedef const GUID *LPCGUID;
+#endif
 #ifndef UUID_DEFINED
 #define UUID_DEFINED
 typedef GUID UUID;
diff --git a/reactos/w32api/include/ddk/scsiwmi.h b/reactos/w32api/include/ddk/scsiwmi.h
index 684271593fe..79bd142d75a 100644
--- a/reactos/w32api/include/ddk/scsiwmi.h
+++ b/reactos/w32api/include/ddk/scsiwmi.h
@@ -60,11 +60,6 @@ typedef struct _GUID {
 } GUID;
 #endif
 
-#ifndef _LPCGUID_DEFINED
-#define _LPCGUID_DEFINED
-typedef const GUID *LPCGUID;
-#endif
-
 typedef struct _SCSIWMIGUIDREGINFO {
   LPCGUID  Guid;
   ULONG  InstanceCount;
diff --git a/reactos/w32api/include/initguid.h b/reactos/w32api/include/initguid.h
index b024c7075f8..aa5e39cf615 100644
--- a/reactos/w32api/include/initguid.h
+++ b/reactos/w32api/include/initguid.h
@@ -8,5 +8,9 @@
 #include <basetyps.h>
 #endif
 #undef DEFINE_GUID
-#define DEFINE_GUID(n,l,w1,w2,b1,b2,b3,b4,b5,b6,b7,b8) GUID_EXT const GUID n GUID_SECT = {l,w1,w2,{b1,b2,b3,b4,b5,b6,b7,b8}}
+#ifdef __cplusplus
+#define DEFINE_GUID(n,l,w1,w2,b1,b2,b3,b4,b5,b6,b7,b8) extern const GUID n GUID_SECT = {l,w1,w2,{b1,b2,b3,b4,b5,b6,b7,b8}}
+#else
+#define DEFINE_GUID(n,l,w1,w2,b1,b2,b3,b4,b5,b6,b7,b8) const GUID n GUID_SECT = {l,w1,w2,{b1,b2,b3,b4,b5,b6,b7,b8}}
+#endif
 #endif