diff --git a/dlls/oleaut32/usrmarshal.c b/dlls/oleaut32/usrmarshal.c
index efab4829c2c..c68eb0dca25 100644
--- a/dlls/oleaut32/usrmarshal.c
+++ b/dlls/oleaut32/usrmarshal.c
@@ -20,6 +20,8 @@
 
 #include <string.h>
 
+#define NONAMELESSUNION
+#define NONAMELESSSTRUCT
 #include "windef.h"
 #include "winbase.h"
 #include "wingdi.h"