diff --git a/contrib/codecs/http/handler.go b/contrib/codecs/http/handler.go
index bc43aa21abe5256587e8fa0ddcd880f85f286746..d03fc660cbe9245c26c1bc1b8e1d53ae30e6fdb3 100644
--- a/contrib/codecs/http/handler.go
+++ b/contrib/codecs/http/handler.go
@@ -20,5 +20,6 @@ func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	c := NewCodec(w, r)
+	w.Header().Set("content-type", contentType)
 	s.Server.ServeCodec(r.Context(), c)
 }