diff --git a/include/rtdef.h b/include/rtdef.h
index 403db780992c69e226b35bc1974590f1c00f5c59..913c8105cf3263338fa2ecee45951939d21d13b8 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,
 };
 
 /**