diff --git a/include/wx/sizer.h b/include/wx/sizer.h
index fcb3a86898..73d99c2779 100644
--- a/include/wx/sizer.h
+++ b/include/wx/sizer.h
@@ -678,7 +678,7 @@ private:
 
 #if wxUSE_STATBOX
 
-class WXDLLEXPORT wxStaticBox;
+#include "wx/statbox.h"
 
 class WXDLLEXPORT wxStaticBoxSizer: public wxBoxSizer
 {