diff --git a/include/types/proto_http.h b/include/types/proto_http.h
index b7b7c6c..5a6cc93 100644
--- a/include/types/proto_http.h
+++ b/include/types/proto_http.h
@@ -197,6 +197,7 @@
 	HTTP_ERR_403,
 	HTTP_ERR_405,
 	HTTP_ERR_408,
+	HTTP_ERR_421,
 	HTTP_ERR_425,
 	HTTP_ERR_429,
 	HTTP_ERR_500,