Make sure that no files except unknwn.h include wine/obj_base.h
directly.

diff --git a/include/oledlg.h b/include/oledlg.h
index 97a089c..0feb8e9 100644
--- a/include/oledlg.h
+++ b/include/oledlg.h
@@ -24,7 +24,7 @@
 #include "commdlg.h"
 #include "prsht.h"
 #include "windef.h"
-#include "oleidl.h"
+#include "ole2.h"
 
 #ifdef __cplusplus
 extern "C" {