diff --git a/include/wx/htmllbox.h b/include/wx/htmllbox.h
index 7f69404903..a65fa566e5 100644
--- a/include/wx/htmllbox.h
+++ b/include/wx/htmllbox.h
@@ -11,6 +11,8 @@
 #ifndef _WX_HTMLLBOX_H_
 #define _WX_HTMLLBOX_H_
 
+#include "wx/defs.h"
+
 #if wxUSE_HTML
 
 #include "wx/vlbox.h"               // base class