diff --git a/include/wx/generic/busyinfo.h b/include/wx/generic/busyinfo.h
index 0151a76b3b..f7cee41bbf 100644
--- a/include/wx/generic/busyinfo.h
+++ b/include/wx/generic/busyinfo.h
@@ -15,6 +15,7 @@
 #if wxUSE_BUSYINFO
 
 class WXDLLIMPEXP_CORE wxFrame;
+class WXDLLIMPEXP_CORE wxWindow;
 
 //--------------------------------------------------------------------------------
 // wxBusyInfo