diff --git a/rpclib-js.opam b/rpclib-js.opam
index 6adfafa2..41609a2e 100644
--- a/rpclib-js.opam
+++ b/rpclib-js.opam
@@ -10,8 +10,8 @@ depends: [
   "ocaml"
   "dune" {>= "1.1.0"}
   "rpclib" {>= "5.0.0"}
-  "js_of_ocaml" {>= "3.3.0"}
-  "js_of_ocaml-ppx" {>= "3.3.0"}
+  "js_of_ocaml" {>= "3.5.0"}
+  "js_of_ocaml-ppx" {>= "3.5.0"}
   "lwt"
 ]
 build: ["dune" "build" "-p" name "-j" jobs]
diff --git a/src/js/rpc_client_js.ml b/src/js/rpc_client_js.ml
index 8e881d27..bcff4f21 100644
--- a/src/js/rpc_client_js.ml
+++ b/src/js/rpc_client_js.ml
@@ -27,7 +27,11 @@ let do_rpc enc dec content_type ~url call =
     Js_of_ocaml.Js.wrap_callback (fun _ ->
         match req ##. readyState with
         | Js_of_ocaml.XmlHttpRequest.DONE ->
-            Lwt.wakeup w (dec (Js_of_ocaml.Js.to_string req ##. responseText))
+            Lwt.wakeup w (dec
+                            (Js_of_ocaml.Js.Opt.case
+                               req##.responseText
+                               (fun () -> "")
+                               (fun x -> Js_of_ocaml.Js.to_string x)))
         | _ -> () ) ;
   req ## send (Js_of_ocaml.Js.some (Js_of_ocaml.Js.string contents)) ;
   Lwt.on_cancel res (fun () -> req ## abort) ;