diff --git a/include/wx/base64.h b/include/wx/base64.h
index 96c6dd80ef..14aaf7d83f 100644
--- a/include/wx/base64.h
+++ b/include/wx/base64.h
@@ -9,6 +9,8 @@
 #ifndef _WX_BASE64_H_
 #define _WX_BASE64_H_
 
+#include "wx/defs.h"
+
 #if wxUSE_BASE64
 
 #include "wx/string.h"