diff --git a/jscomp/others/node_fs.ml b/jscomp/others/node_fs.ml
index d0640bea9..14ca2ed80 100644
--- a/jscomp/others/node_fs.ml
+++ b/jscomp/others/node_fs.ml
@@ -67,7 +67,7 @@ module Watch = struct
     f:
       ([ `change of
          (string (*eventType*) -> Node.string_buffer (* filename *) -> unit[@u])
-       | `error of (unit -> unit[@u]) ]
+       | `error of (unit -> unit[@u0]) ]
       [@mel.string]) ->
     t = "on"
   [@@mel.send]
diff --git a/jscomp/runtime/caml_external_polyfill.ml b/jscomp/runtime/caml_external_polyfill.ml
index 7f668f78e..fd11ced25 100644
--- a/jscomp/runtime/caml_external_polyfill.ml
+++ b/jscomp/runtime/caml_external_polyfill.ml
@@ -28,7 +28,7 @@ open struct
   module Js = Js_internal
 end
 
-let getGlobalThis : (unit -> global[@u]) =
+let getGlobalThis : (unit -> global[@u0]) =
   [%raw
     {| function(){
   if (typeof globalThis !== 'undefined') return globalThis;
diff --git a/jscomp/stdlib/camlinternalLazy.ml b/jscomp/stdlib/camlinternalLazy.ml
index 61edcf460..5414ee9ab 100644
--- a/jscomp/stdlib/camlinternalLazy.ml
+++ b/jscomp/stdlib/camlinternalLazy.ml
@@ -36,8 +36,8 @@ type 'a concrete = {
 
 exception Undefined
 
-external fnToVal : (unit -> 'a [@u]) -> 'a = "%identity"
-external valToFn :  'a -> (unit -> 'a [@u])  = "%identity"
+external fnToVal : (unit -> 'a [@u0]) -> 'a = "%identity"
+external valToFn :  'a -> (unit -> 'a [@u0])  = "%identity"
 external castToConcrete : 'a lazy_t -> 'a concrete   = "%identity"
 external of_concrete : 'a concrete -> 'a lazy_t   = "%identity"
 
@@ -46,15 +46,15 @@ let is_val (type a ) (l : a lazy_t) : bool =
 
 
 
-let forward_with_closure (type a ) (blk : a concrete) (closure : unit -> a [@u]) : a =
-  let result = closure () [@u] in
+let forward_with_closure (type a ) (blk : a concrete) (closure : unit -> a [@u0]) : a =
+  let result = closure () [@u0] in
   (* do set_field BEFORE set_tag *)
   blk.value <- result;
   blk.tag<- true;
   result
 
 
-let raise_undefined =  (fun [@u] () -> raise Undefined)
+let raise_undefined =  (fun [@u0] () -> raise Undefined)
 
 (* Assume [blk] is a block with tag lazy *)
 let force_lazy_block (type a ) (blk : a t) : a  =
@@ -64,7 +64,7 @@ let force_lazy_block (type a ) (blk : a t) : a  =
   try
     forward_with_closure blk closure
   with e ->
-    blk.value <- fnToVal (fun [@u] () -> raise e);
+    blk.value <- fnToVal (fun [@u0] () -> raise e);
     raise e
 
 
diff --git a/jscomp/test/demo.ml b/jscomp/test/demo.ml
index fee9fe057..e89e094ff 100644
--- a/jscomp/test/demo.ml
+++ b/jscomp/test/demo.ml
@@ -94,7 +94,7 @@ let ui_layout
       with  e -> ()
     end;
     let fmt v = toFixed v 2 in
-    set_interval (fun [@u] () ->
+    set_interval (fun [@u0] () ->
 
       grid##dataSource #=
         ( array_map data (fun [@u] {ticker; price } ->
diff --git a/jscomp/test/demo_binding.ml b/jscomp/test/demo_binding.ml
index 6dc23ce64..e77dbeec1 100644
--- a/jscomp/test/demo_binding.ml
+++ b/jscomp/test/demo_binding.ml
@@ -102,7 +102,7 @@ class type textArea =
   end[@u]
 
 
-external set_interval : (unit -> unit [@u]) -> float -> unit  =  "setInterval"
+external set_interval : (unit -> unit [@u0]) -> float -> unit  =  "setInterval"
      [@@mel.module "@runtime", "Runtime"]
 
 external toFixed : float -> int -> string = "toFixed" [@@mel.send]
diff --git a/jscomp/test/dist/jscomp/test/event_ffi.js b/jscomp/test/dist/jscomp/test/event_ffi.js
index a2847be6f..470821e5d 100644
--- a/jscomp/test/dist/jscomp/test/event_ffi.js
+++ b/jscomp/test/dist/jscomp/test/event_ffi.js
@@ -5,11 +5,11 @@ var Curry = require("melange.js/curry.js");
 var Stdlib__List = require("melange/list.js");
 
 function h0(x) {
-  return x();
+  return x(undefined);
 }
 
 function h00(x) {
-  return x();
+  return x(undefined);
 }
 
 function h1(x, y) {
@@ -39,7 +39,7 @@ function ocaml_run(b, c) {
   return (x + b | 0) + c | 0;
 }
 
-function a0() {
+function a0(param) {
   console.log("hi");
 }
 
diff --git a/jscomp/test/dist/jscomp/test/exception_raise_test.js b/jscomp/test/dist/jscomp/test/exception_raise_test.js
index 4e5222398..ccdf6afc7 100644
--- a/jscomp/test/dist/jscomp/test/exception_raise_test.js
+++ b/jscomp/test/dist/jscomp/test/exception_raise_test.js
@@ -196,7 +196,7 @@ function eq(loc, x, y) {
 
 try {
   ((()=>{throw 2}
-      )());
+      )(undefined));
 }
 catch (raw_e$2){
   var e = Caml_js_exceptions.internalToOCamlException(raw_e$2);
diff --git a/jscomp/test/dist/jscomp/test/ffi_arity_test.js b/jscomp/test/dist/jscomp/test/ffi_arity_test.js
index 12b5daa48..8e9a99f42 100644
--- a/jscomp/test/dist/jscomp/test/ffi_arity_test.js
+++ b/jscomp/test/dist/jscomp/test/ffi_arity_test.js
@@ -40,7 +40,7 @@ var hh = [
       return parseInt(x);
     });
 
-function u() {
+function u(param) {
   return 3;
 }
 
@@ -54,8 +54,8 @@ function fff(param) {
   vvv.contents = vvv.contents + 1 | 0;
 }
 
-function g() {
-  return fff(undefined);
+function g(param) {
+  fff(undefined);
 }
 
 function abc(x, y, z) {
@@ -66,7 +66,7 @@ function abc(x, y, z) {
 
 var abc_u = abc;
 
-g();
+g(undefined);
 
 Mt.from_pair_suites("Ffi_arity_test", {
       hd: [
diff --git a/jscomp/test/dist/jscomp/test/ocaml_parsetree_test.js b/jscomp/test/dist/jscomp/test/ocaml_parsetree_test.js
index 93de45ca1..3c858e244 100644
--- a/jscomp/test/dist/jscomp/test/ocaml_parsetree_test.js
+++ b/jscomp/test/dist/jscomp/test/ocaml_parsetree_test.js
@@ -2042,56 +2042,56 @@ function from_pair_suites(name, suites) {
   var match = Stdlib__Array.to_list(Process.argv);
   if (match) {
     if (is_mocha(undefined)) {
-      describe(name, (function () {
-              return Stdlib__List.iter((function (param) {
-                            var code = param[1];
-                            it(param[0], (function () {
-                                    var spec = Curry._1(code, undefined);
-                                    switch (spec.TAG | 0) {
-                                      case /* Eq */0 :
-                                          Assert.deepEqual(spec._0, spec._1);
-                                          return ;
-                                      case /* Neq */1 :
-                                          Assert.notDeepEqual(spec._0, spec._1);
-                                          return ;
-                                      case /* StrictEq */2 :
-                                          Assert.strictEqual(spec._0, spec._1);
-                                          return ;
-                                      case /* StrictNeq */3 :
-                                          Assert.notStrictEqual(spec._0, spec._1);
-                                          return ;
-                                      case /* Ok */4 :
-                                          Assert.ok(spec._0);
-                                          return ;
-                                      case /* Approx */5 :
-                                          var b = spec._1;
-                                          var a = spec._0;
-                                          if (!close_enough(undefined, a, b)) {
-                                            Assert.deepEqual(a, b);
-                                            return ;
-                                          } else {
-                                            return ;
-                                          }
-                                      case /* ApproxThreshold */6 :
-                                          var b$1 = spec._2;
-                                          var a$1 = spec._1;
-                                          if (!close_enough(spec._0, a$1, b$1)) {
-                                            Assert.deepEqual(a$1, b$1);
-                                            return ;
-                                          } else {
-                                            return ;
-                                          }
-                                      case /* ThrowAny */7 :
-                                          Assert.throws(spec._0);
-                                          return ;
-                                      case /* Fail */8 :
-                                          return assert_fail("failed");
-                                      case /* FailWith */9 :
-                                          return assert_fail(spec._0);
-                                      
+      describe(name, (function (param) {
+              Stdlib__List.iter((function (param) {
+                      var code = param[1];
+                      it(param[0], (function () {
+                              var spec = Curry._1(code, undefined);
+                              switch (spec.TAG | 0) {
+                                case /* Eq */0 :
+                                    Assert.deepEqual(spec._0, spec._1);
+                                    return ;
+                                case /* Neq */1 :
+                                    Assert.notDeepEqual(spec._0, spec._1);
+                                    return ;
+                                case /* StrictEq */2 :
+                                    Assert.strictEqual(spec._0, spec._1);
+                                    return ;
+                                case /* StrictNeq */3 :
+                                    Assert.notStrictEqual(spec._0, spec._1);
+                                    return ;
+                                case /* Ok */4 :
+                                    Assert.ok(spec._0);
+                                    return ;
+                                case /* Approx */5 :
+                                    var b = spec._1;
+                                    var a = spec._0;
+                                    if (!close_enough(undefined, a, b)) {
+                                      Assert.deepEqual(a, b);
+                                      return ;
+                                    } else {
+                                      return ;
+                                    }
+                                case /* ApproxThreshold */6 :
+                                    var b$1 = spec._2;
+                                    var a$1 = spec._1;
+                                    if (!close_enough(spec._0, a$1, b$1)) {
+                                      Assert.deepEqual(a$1, b$1);
+                                      return ;
+                                    } else {
+                                      return ;
                                     }
-                                  }));
-                          }), suites);
+                                case /* ThrowAny */7 :
+                                    Assert.throws(spec._0);
+                                    return ;
+                                case /* Fail */8 :
+                                    return assert_fail("failed");
+                                case /* FailWith */9 :
+                                    return assert_fail(spec._0);
+                                
+                              }
+                            }));
+                    }), suites);
             }));
       return ;
     } else {
diff --git a/jscomp/test/dist/jscomp/test/ppx_apply_test.js b/jscomp/test/dist/jscomp/test/ppx_apply_test.js
index 04694dcd3..ae7d13de8 100644
--- a/jscomp/test/dist/jscomp/test/ppx_apply_test.js
+++ b/jscomp/test/dist/jscomp/test/ppx_apply_test.js
@@ -30,7 +30,7 @@ function eq(loc, x, y) {
 
 var u = 3;
 
-function nullary() {
+function nullary(param) {
   return 3;
 }
 
diff --git a/jscomp/test/dist/jscomp/test/raw_output_test.js b/jscomp/test/dist/jscomp/test/raw_output_test.js
index be06893a9..a1974236a 100644
--- a/jscomp/test/dist/jscomp/test/raw_output_test.js
+++ b/jscomp/test/dist/jscomp/test/raw_output_test.js
@@ -10,9 +10,9 @@ function mk(fn) {
 (((_)=> console.log('should works')
     )(undefined));
 
-console.log((function () {
+console.log((function (param) {
           return 1;
-        })());
+        })(undefined));
 
 exports.mk = mk;
 /*  Not a pure module */
diff --git a/jscomp/test/dist/jscomp/test/re_or_res/reactTestUtils.js b/jscomp/test/dist/jscomp/test/re_or_res/reactTestUtils.js
index 5c9543624..f3ff88ef9 100644
--- a/jscomp/test/dist/jscomp/test/re_or_res/reactTestUtils.js
+++ b/jscomp/test/dist/jscomp/test/re_or_res/reactTestUtils.js
@@ -8,14 +8,14 @@ var Curry = require("melange.js/curry.js");
 var TestUtils = require("react-dom/test-utils");
 
 function act(func) {
-  var reactFunc = function () {
+  var reactFunc = function (param) {
     Curry._1(func, undefined);
   };
   TestUtils.act(reactFunc);
 }
 
 function actAsync(func) {
-  return TestUtils.act(function () {
+  return TestUtils.act(function (param) {
               return Curry._1(func, undefined);
             });
 }
diff --git a/jscomp/test/dist/jscomp/test/uncurry_glob_test.js b/jscomp/test/dist/jscomp/test/uncurry_glob_test.js
index f8ce2fb1f..67cd5f61c 100644
--- a/jscomp/test/dist/jscomp/test/uncurry_glob_test.js
+++ b/jscomp/test/dist/jscomp/test/uncurry_glob_test.js
@@ -9,11 +9,11 @@ function M(U) {
         };
 }
 
-function f() {
+function f(param) {
   return 3;
 }
 
-f();
+f(undefined);
 
 function $plus$great(a, h) {
   return h(a);
diff --git a/jscomp/test/gpr_2682_test.ml b/jscomp/test/gpr_2682_test.ml
index 70523f9de..a09359f30 100644
--- a/jscomp/test/gpr_2682_test.ml
+++ b/jscomp/test/gpr_2682_test.ml
@@ -52,9 +52,8 @@ end
 ;;   forIn   [%obj{x = 3 ; y = 3}]  (fun[@u] x -> Js.log x)
 
 
-let f3  : unit -> bool [@u] = [%raw"()=>true"]
+let f3  : unit -> bool [@u0] = [%raw"()=>true"]
 
-let bbbb  = f3 () [@u]
+let bbbb  = f3 () [@u0]
 
 ;;assert (bbbb)
-
diff --git a/jscomp/test/http_types.ml b/jscomp/test/http_types.ml
index df1e866ec..fa49571ed 100644
--- a/jscomp/test/http_types.ml
+++ b/jscomp/test/http_types.ml
@@ -23,7 +23,7 @@ class type _resp =
 type resp = _resp Js.t
 class type _server =
   object
-    method listen : int ->  string -> (unit -> unit [@u]) -> unit
+    method listen : int ->  string -> (unit -> unit [@u0]) -> unit
   end[@u]
 type server = _server Js.t
 class type _http =
diff --git a/jscomp/test/mt.ml b/jscomp/test/mt.ml
index 22171618a..ce1f5ae37 100644
--- a/jscomp/test/mt.ml
+++ b/jscomp/test/mt.ml
@@ -1,4 +1,4 @@
-external describe : string -> (unit -> unit[@u]) -> unit = "describe"
+external describe : string -> (unit -> unit[@u0]) -> unit = "describe"
 
 external it : string -> (unit -> unit[@mel.uncurry]) -> unit = "it"
 external it_promise : string -> (unit -> _ Js.Promise.t [@mel.uncurry]) -> unit = "it"
@@ -37,7 +37,7 @@ let from_suites name (suite :  (string * ('a -> unit)) list) =
   match Array.to_list Node.Process.process##argv with
   | _cmd :: _ ->
     if is_mocha () then
-      describe name (fun [@u] () ->
+      describe name (fun [@u0] () ->
           List.iter (fun (name, code) -> it name code) suite)
 
   | _ -> ()
@@ -96,7 +96,7 @@ let from_pair_suites name (suites :  pair_suites) =
   match Array.to_list Node.Process.process##argv with
   | _cmd :: _ ->
     if is_mocha () then
-      describe name (fun [@u] () ->
+      describe name (fun [@u0] () ->
           suites |>
           List.iter (fun (name, code) ->
               it name (fun _ ->
@@ -111,7 +111,7 @@ let from_promise_suites name (suites : (string * _ Js.Promise.t ) list) =
   match Array.to_list Node.Process.process##argv with
   | _cmd :: _ ->
     if is_mocha () then
-      describe name (fun [@u] () ->
+      describe name (fun [@u0] () ->
           suites |>
           List.iter (fun (name, code) ->
               it_promise name (fun _ ->
diff --git a/jscomp/test/ocaml_typedtree_test.ml b/jscomp/test/ocaml_typedtree_test.ml
index be366f210..a288d5707 100644
--- a/jscomp/test/ocaml_typedtree_test.ml
+++ b/jscomp/test/ocaml_typedtree_test.ml
@@ -11621,7 +11621,7 @@ end = struct
 
 
 
-external describe : string -> (unit -> unit[@u]) -> unit = "describe"
+external describe : string -> (unit -> unit[@u0]) -> unit = "describe"
 
 
 external it : string -> (unit -> unit[@mel.uncurry]) -> unit = "it"
@@ -11677,7 +11677,7 @@ let from_suites name (suite :  (string * ('a -> unit)) list) =
   match Array.to_list Node.Process.process##argv with
   | cmd :: _ ->
     if is_mocha () then
-      describe name (fun [@u] () ->
+      describe name (fun [@u0] () ->
           List.iter (fun (name, code) -> it name code) suite)
 
   | _ -> ()
@@ -11736,7 +11736,7 @@ let from_pair_suites name (suites :  pair_suites) =
   match Array.to_list Node.Process.process##argv with
   | cmd :: _ ->
     if is_mocha () then
-      describe name (fun [@u] () ->
+      describe name (fun [@u0] () ->
           suites |>
           List.iter (fun (name, code) ->
               it name (fun _ ->
@@ -11751,7 +11751,7 @@ let from_promise_suites name (suites : (string * _ Js.Promise.t ) list) =
   match Array.to_list Node.Process.process##argv with
   | cmd :: _ ->
     if is_mocha () then
-      describe name (fun [@u] () ->
+      describe name (fun [@u0] () ->
           suites |>
           List.iter (fun (name, code) ->
               it_promise name (fun _ ->
diff --git a/jscomp/test/pipe_send_readline.ml b/jscomp/test/pipe_send_readline.ml
index 2295841ef..1bf2f4915 100644
--- a/jscomp/test/pipe_send_readline.ml
+++ b/jscomp/test/pipe_send_readline.ml
@@ -1,18 +1,17 @@
-
 (*  should give a warning on unused attribute..   [@@mel.xx] *)
 
 
 type readline
 external on :
   ([ `line of (string -> unit [@u])
-   | `close of (unit -> unit [@u])]
+   | `close of (unit -> unit [@u0])]
      [@mel.string]) ->
   'self =
   "on" [@@mel.send.pipe:readline as 'self]
 let u rl =
   rl
   |> on (`line (fun [@u] x -> Js.log x ))
-  |> on (`close (fun [@u] () -> Js.log "finished"))
+  |> on (`close (fun [@u0] () -> Js.log "finished"))
 
 
 
diff --git a/jscomp/test/test_http_server.ml b/jscomp/test/test_http_server.ml
index 485eee4f0..7903e93e6 100644
--- a/jscomp/test/test_http_server.ml
+++ b/jscomp/test/test_http_server.ml
@@ -1,6 +1,3 @@
-
-
-
 let port = 3000
 let hostname = "127.0.0.1"
 let create_server  http =
@@ -9,11 +6,10 @@ let create_server  http =
       resp##setHeader "Content-Type" "text/plain";
       resp##_end "Hello world\n"
     end in
-  server##listen port hostname  begin fun [@u] () ->
+  server##listen port hostname  begin fun [@u0] () ->
     Js.log ("Server running at http://"^ hostname ^ ":" ^ string_of_int port ^ "/")
   end
 
 let () =
   create_server Http_types.http
 
-
diff --git a/jscomp/test/tramp_fib.ml b/jscomp/test/tramp_fib.ml
index 05d83dfb5..a0b187589 100644
--- a/jscomp/test/tramp_fib.ml
+++ b/jscomp/test/tramp_fib.ml
@@ -5,7 +5,7 @@ let test_id = ref 0
 let eq loc x y = Mt.eq_suites ~test_id ~suites loc x y
 
 
-type 'a bounce = Continue of 'a | Suspend of (unit -> 'a bounce [@u])
+type 'a bounce = Continue of 'a | Suspend of (unit -> 'a bounce [@u0])
 (* https://eli.thegreenplace.net/2017/on-recursion-continuations-and-trampolines/ *)
 (* http://gallium.inria.fr/seminaires/transparents/20141027.Frederic.Bour.pdf *)
 (* http://www.usrsb.in/blog/blog/2012/08/12/bouncing-pythons-generators-with-a-trampoline/ *)
@@ -17,7 +17,7 @@ let rec fib n k =
     (* Suspend (fun [@u]() -> k (Continue 1 ) [@u]) *)
     k 1 [@u]
   | _ ->
-    Suspend (fun [@u] () ->
+    Suspend (fun [@u0] () ->
       fib (n-1) (fun [@u] v0 ->
         fib (n-2) (fun [@u] v1 ->
           k (v0 + v1) [@u]
@@ -37,7 +37,7 @@ let u = fib 10 (fun [@u] x -> Continue x)
 let rec iter (bounce : 'a bounce) : 'a =
   match bounce with
   | Continue v -> v
-  | Suspend f -> iter (f () [@u])
+  | Suspend f -> iter (f () [@u0])
 
 
 (* first it needs to be tailcall *)
@@ -45,7 +45,7 @@ let rec isEven n =
   match n with
   | 0 -> Continue true
   | 1 -> Continue false
-  | _ -> Suspend (fun [@u] () -> isOdd (n - 1))
+  | _ -> Suspend (fun [@u0] () -> isOdd (n - 1))
 and isOdd n =
   match n with
   | 0 -> Continue false
diff --git a/jscomp/test/uncurry_test.ml b/jscomp/test/uncurry_test.ml
index c514a5552..812c61166 100644
--- a/jscomp/test/uncurry_test.ml
+++ b/jscomp/test/uncurry_test.ml
@@ -1,6 +1,6 @@
 type ('a0, 'a1) t = ('a0 -> 'a1 [@u])
 
-let f0 = fun [@u] () -> 0
+let f0 = fun [@u0] () -> 0
 let f1 = fun [@u] a0 -> a0
 let f2 = fun [@u] a0 a1 -> (a0,a1)
 let f3= fun [@u]a0 a1 a2 -> ( a0,a1,a2)
@@ -25,7 +25,7 @@ let f21= fun [@u]a0 a1 a2 a3 a4 a5 a6 a7 a8 a9 a10 a11 a12 a13 a14 a15 a16 a17 a
 let f22= fun [@u]a0 a1 a2 a3 a4 a5 a6 a7 a8 a9 a10 a11 a12 a13 a14 a15 a16 a17 a18 a19 a20 a21 -> ( a0,a1,a2,a3,a4,a5,a6,a7,a8,a9,a10,a11,a12,a13,a14,a15,a16,a17,a18,a19,a20,a21)
 (* let f23= fun [@u]a0 a1 a2 a3 a4 a5 a6 a7 a8 a9 a10 a11 a12 a13 a14 a15 a16 a17 a18 a19 a20 a21 a22 -> ( a0,a1,a2,a3,a4,a5,a6,a7,a8,a9,a10,a11,a12,a13,a14,a15,a16,a17,a18,a19,a20,a21) *)
 (* TODO: better errror message than Unbound record field Js.Fn.I_23 *)
-;; f0 () [@u] |. Js.log
+;; f0 () [@u0] |. Js.log
 ;; f1 0 [@u] |. Js.log
 
 ;; f2 0 1 [@u] |. Js.log
@@ -50,4 +50,4 @@ let f22= fun [@u]a0 a1 a2 a3 a4 a5 a6 a7 a8 a9 a10 a11 a12 a13 a14 a15 a16 a17 a
 ;; f21 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 [@u] |. Js.log
 ;; f22 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 [@u] |. Js.log
 
-let rec xx = fun [@u] () -> xx () [@u]
+let rec xx = fun [@u0] () -> xx () [@u0]
diff --git a/jscomp/test/uncurry_test.mli b/jscomp/test/uncurry_test.mli
index 97493544d..3246e4303 100644
--- a/jscomp/test/uncurry_test.mli
+++ b/jscomp/test/uncurry_test.mli
@@ -1,5 +1,5 @@
 type ('a0, 'a1) t = ('a0 -> 'a1 [@u])
-val f0 : (unit -> int [@u])
+val f0 : (unit -> int [@u0])
 val f1 : ('a -> 'a [@u])
 val f2 : ('a -> 'b -> 'a * 'b [@u])
 val f3 : ('a -> 'b -> 'c -> 'a * 'b * 'c [@u])
@@ -265,4 +265,4 @@ val f22 :
    'p * 'q * 'r * 's * 't * 'u * 'v
   [@u])
 
-val xx : unit -> 'a [@u]
+val xx : unit -> 'a [@u0]