diff --git a/include/wx/mdi.h b/include/wx/mdi.h
index 2165d1a1fe..3223c7cb2e 100644
--- a/include/wx/mdi.h
+++ b/include/wx/mdi.h
@@ -1,6 +1,8 @@
 #ifndef _WX_MDI_H_BASE_
 #define _WX_MDI_H_BASE_
 
+#include "wx/setup.h"
+
 #if wxUSE_MDI_ARCHITECTURE
 
 #if defined(__WXUNIVERSAL__)