diff --git a/include/wx/msw/ole/activex.h b/include/wx/msw/ole/activex.h
index e0624f16ae..2436e7933b 100644
--- a/include/wx/msw/ole/activex.h
+++ b/include/wx/msw/ole/activex.h
@@ -27,6 +27,8 @@
 #include "wx/window.h"
 #include "wx/variant.h"
 
+class FrameSite;
+
 //---------------------------------------------------------------------------
 // MSW COM includes
 //---------------------------------------------------------------------------