diff --git a/include/rtdef.h b/include/rtdef.h
index 403db78099..913c8105cf 100644
--- a/include/rtdef.h
+++ b/include/rtdef.h
@@ -895,6 +895,7 @@ enum
     RTGRAPHIC_PIXEL_FORMAT_RGB888,
     RTGRAPHIC_PIXEL_FORMAT_ARGB888,
     RTGRAPHIC_PIXEL_FORMAT_ABGR888,
+    RTGRAPHIC_PIXEL_FORMAT_ALPHA,
 };
 
 /**