diff -uNr ppx_sexp_message-113.33.00/_oasis ppx_sexp_message-113.33.00+4.03/_oasis
--- ppx_sexp_message-113.33.00/_oasis	2016-03-09 16:44:54.000000000 +0100
+++ ppx_sexp_message-113.33.00+4.03/_oasis	2016-03-22 15:13:51.000000000 +0100
@@ -1,8 +1,8 @@
 OASISFormat:      0.4
-OCamlVersion:     >= 4.02.3
+OCamlVersion:     >= 4.03.0
 FindlibVersion:   >= 1.3.2
 Name:             ppx_sexp_message
-Version:          113.33.00
+Version:          113.33.00+4.03
 Synopsis:         A ppx rewriter for easy construction of s-expressions
 Authors:          Jane Street Group, LLC <opensource@janestreet.com>
 Copyrights:       (C) 2015-2016 Jane Street Group LLC <opensource@janestreet.com>
diff -uNr ppx_sexp_message-113.33.00/opam ppx_sexp_message-113.33.00+4.03/opam
--- ppx_sexp_message-113.33.00/opam	2016-03-18 12:08:01.000000000 +0100
+++ ppx_sexp_message-113.33.00+4.03/opam	2016-03-22 17:51:37.000000000 +0100
@@ -18,4 +18,4 @@
   "ppx_sexp_conv"
   "ppx_tools"     {>= "0.99.3"}
 ]
-available: [ ocaml-version >= "4.02.3" ]
+available: [ ocaml-version >= "4.03.0" ]
diff -uNr ppx_sexp_message-113.33.00/src/ppx_sexp_message.ml ppx_sexp_message-113.33.00+4.03/src/ppx_sexp_message.ml
--- ppx_sexp_message-113.33.00/src/ppx_sexp_message.ml	2016-03-09 16:44:54.000000000 +0100
+++ ppx_sexp_message-113.33.00+4.03/src/ppx_sexp_message.ml	2016-03-22 15:13:51.000000000 +0100
@@ -42,13 +42,10 @@
     eapply ~loc (evar ~loc ("Sexplib.Conv.sexp_of_" ^ typ)) [pexp_constant ~loc const]
   in
   match const with
-  | Const_int       _ -> f "int"
-  | Const_char      _ -> f "char"
-  | Const_string    _ -> f "string"
-  | Const_float     _ -> f "float"
-  | Const_int32     _ -> f "int32"
-  | Const_int64     _ -> f "int64"
-  | Const_nativeint _ -> f "nativeint"
+  | Pconst_integer       _ -> f "int"
+  | Pconst_char      _ -> f "char"
+  | Pconst_string    _ -> f "string"
+  | Pconst_float     _ -> f "float"
 ;;
 
 let rewrite_here e =
@@ -62,7 +59,7 @@
   let e = rewrite_here e in
   let loc = e.pexp_loc in
   match e.pexp_desc with
-  | Pexp_constant (Const_string ("", _)) ->
+  | Pexp_constant (Pconst_string ("", _)) ->
     None
   | Pexp_constant const ->
     Some (sexp_of_constant ~loc const)
@@ -71,18 +68,6 @@
   | _ -> Some [%expr Sexplib.Conv.sexp_of_string [%e e]]
 ;;
 
-type arg_label =
-  | Nolabel
-  | Labelled of string
-  | Optional
-
-(* Will help with the switch to 4.03 *)
-let arg_label_of_string = function
-  | "" -> Nolabel
-  | s when s.[0] = '?' -> Optional
-  | s -> Labelled s
-;;
-
 let sexp_of_labelled_expr (label, e) =
   let loc = e.pexp_loc in
   match label, e.pexp_desc with
@@ -97,7 +82,7 @@
   | Labelled label, _ ->
     Some (sexp_inline ~loc (sexp_atom ~loc (estring ~loc label)
                             :: List.of_option (sexp_of_expr e)))
-  | Optional, _ ->
+  | Optional _, _ ->
     (* Could be used to encode sexp_option if that's ever needed. *)
     Location.raise_errorf ~loc
       "ppx_sexp_value: optional argument not allowed here"
@@ -112,7 +97,7 @@
   let labelled_exprs =
     match e.pexp_desc with
     | Pexp_apply (f, args) ->
-      (Nolabel, f) :: List.map args ~f:(fun (label, e) -> arg_label_of_string label, e)
+      (Nolabel, f) :: args
     | _ ->
       (Nolabel, e) :: []
   in