diff --git a/sdk/xtdk/xtdefs.h b/sdk/xtdk/xtdefs.h
index b972002..411a550 100644
--- a/sdk/xtdk/xtdefs.h
+++ b/sdk/xtdk/xtdefs.h
@@ -23,6 +23,7 @@
 #define EXTERN                                  extern
 #define STRUCT                                  struct
 #define STATIC                                  static
+#define UNION                                   union
 #define VOLATILE                                volatile
 
 /* NULL values */