diff --git a/binaryen.opam b/binaryen.opam
index b97829e8..25033cba 100644
--- a/binaryen.opam
+++ b/binaryen.opam
@@ -15,6 +15,6 @@ depends: [
   "ocaml" {>= "4.13.0"}
   "dune" {>= "3.0.0"}
   "dune-configurator" {>= "3.0.0"}
-  "js_of_ocaml-compiler" {>= "4.1.0" < "6.0.0"}
+  "js_of_ocaml-compiler" {>= "6.0.0" < "7.0.0"}
   "libbinaryen" {>= "116.0.0" < "117.0.0"}
 ]
diff --git a/esy.lock/index.json b/esy.lock/index.json
index 0b767567..a98378b1 100644
--- a/esy.lock/index.json
+++ b/esy.lock/index.json
@@ -1,5 +1,5 @@
 {
-  "checksum": "ad7ec1c1f18f2da0d805bf4ce5a7f697",
+  "checksum": "027362814c85d00422b9f9ff4957739b",
   "root": "@grain/binaryen.ml@link-dev:./package.json",
   "node": {
     "ocaml@4.14.1000@d41d8cd9": {
@@ -1039,20 +1039,20 @@
       ],
       "available": "true"
     },
-    "@opam/js_of_ocaml-compiler@opam:5.9.1@e8650b39": {
-      "id": "@opam/js_of_ocaml-compiler@opam:5.9.1@e8650b39",
+    "@opam/js_of_ocaml-compiler@opam:6.0.1@ac2ae2e8": {
+      "id": "@opam/js_of_ocaml-compiler@opam:6.0.1@ac2ae2e8",
       "name": "@opam/js_of_ocaml-compiler",
-      "version": "opam:5.9.1",
+      "version": "opam:6.0.1",
       "source": {
         "type": "install",
         "source": [
-          "archive:https://opam.ocaml.org/cache/sha256/68/68c95c60871d8e9c9a54c82f35e2ed50413bcb440f220d0b3516b2a1ee1c7307#sha256:68c95c60871d8e9c9a54c82f35e2ed50413bcb440f220d0b3516b2a1ee1c7307",
-          "archive:https://github.com/ocsigen/js_of_ocaml/releases/download/5.9.1/js_of_ocaml-5.9.1.tbz#sha256:68c95c60871d8e9c9a54c82f35e2ed50413bcb440f220d0b3516b2a1ee1c7307"
+          "archive:https://opam.ocaml.org/cache/sha256/81/813dbee2b62e1541049ea23a20e405cf244e27ebfa9859785cfa53e286d2c614#sha256:813dbee2b62e1541049ea23a20e405cf244e27ebfa9859785cfa53e286d2c614",
+          "archive:https://github.com/ocsigen/js_of_ocaml/releases/download/6.0.1/js_of_ocaml-6.0.1.tbz#sha256:813dbee2b62e1541049ea23a20e405cf244e27ebfa9859785cfa53e286d2c614"
         ],
         "opam": {
           "name": "js_of_ocaml-compiler",
-          "version": "5.9.1",
-          "path": "esy.lock/opam/js_of_ocaml-compiler.5.9.1"
+          "version": "6.0.1",
+          "path": "esy.lock/opam/js_of_ocaml-compiler.6.0.1"
         }
       },
       "overrides": [],
@@ -1648,7 +1648,7 @@
       "devDependencies": [
         "@opam/ocamlformat@opam:0.24.1@01d7df0f",
         "@opam/ocaml-lsp-server@opam:1.12.4@c24ab770",
-        "@opam/js_of_ocaml-compiler@opam:5.9.1@e8650b39"
+        "@opam/js_of_ocaml-compiler@opam:6.0.1@ac2ae2e8"
       ]
     },
     "@esy-ocaml/substs@0.0.1@d41d8cd9": {
diff --git a/esy.lock/opam/js_of_ocaml-compiler.5.9.1/opam b/esy.lock/opam/js_of_ocaml-compiler.6.0.1/opam
similarity index 72%
rename from esy.lock/opam/js_of_ocaml-compiler.5.9.1/opam
rename to esy.lock/opam/js_of_ocaml-compiler.6.0.1/opam
index 89af4b17..ed835fe8 100644
--- a/esy.lock/opam/js_of_ocaml-compiler.5.9.1/opam
+++ b/esy.lock/opam/js_of_ocaml-compiler.6.0.1/opam
@@ -11,10 +11,10 @@ homepage: "https://ocsigen.org/js_of_ocaml/latest/manual/overview"
 doc: "https://ocsigen.org/js_of_ocaml/latest/manual/overview"
 bug-reports: "https://github.com/ocsigen/js_of_ocaml/issues"
 depends: [
-  "dune" {>= "3.15"}
+  "dune" {>= "3.17"}
   "ocaml" {>= "4.08" & < "5.4"}
   "num" {with-test}
-  "ppx_expect" {>= "v0.14.2" & with-test}
+  "ppx_expect" {>= "v0.16.1" & with-test}
   "ppxlib" {>= "0.15.0" & < "0.36.0"}
   "re" {with-test}
   "cmdliner" {>= "1.1.0"}
@@ -23,7 +23,7 @@ depends: [
   "menhir"
   "menhirLib"
   "menhirSdk"
-  "yojson" {>= "1.6"}
+  "yojson" {>= "2.1"}
   "odoc" {with-doc}
 ]
 depopts: ["ocamlfind"]
@@ -47,10 +47,10 @@ build: [
 ]
 url {
   src:
-    "https://github.com/ocsigen/js_of_ocaml/releases/download/5.9.1/js_of_ocaml-5.9.1.tbz"
+    "https://github.com/ocsigen/js_of_ocaml/releases/download/6.0.1/js_of_ocaml-6.0.1.tbz"
   checksum: [
-    "sha256=68c95c60871d8e9c9a54c82f35e2ed50413bcb440f220d0b3516b2a1ee1c7307"
-    "sha512=288d68ea7a45e92375cf51c34bb1071dd26d0d8de54883f3422639561e1494ff43aa45c3d7466627fd7b5a9bb29a0c75e5744a3e7147f5d544bf2c5414083778"
+    "sha256=813dbee2b62e1541049ea23a20e405cf244e27ebfa9859785cfa53e286d2c614"
+    "sha512=194ae5d1122171fa8253b6a41438a2fc330caf4ab6dd008fcce1253fd51fbe4b1149813da6075c5deb52ea136143def57c83c3f4e32421803d7699648fdc563b"
   ]
 }
-x-commit-hash: "a02342914f3221a298730d61537cc0d939ccb6e0"
+x-commit-hash: "b6d60e4f8ff35e7c7b3bb52b97ffedc3eb8e3d08"
diff --git a/package.json b/package.json
index 69a9bb85..a042d0e8 100644
--- a/package.json
+++ b/package.json
@@ -11,7 +11,7 @@
     "@opam/dune-configurator": ">= 3.0.0"
   },
   "devDependencies": {
-    "@opam/js_of_ocaml-compiler": ">= 4.1.0 < 6.0.0",
+    "@opam/js_of_ocaml-compiler": ">= 6.0.0 < 7.0.0",
     "@opam/ocamlformat": "0.24.1",
     "@opam/ocaml-lsp-server": ">= 1.9.1 < 1.13.0"
   },
diff --git a/src/expression.js b/src/expression.js
index 50dc0da1..fa8c8332 100644
--- a/src/expression.js
+++ b/src/expression.js
@@ -882,11 +882,12 @@ function caml_binaryen_expression_id_array_len() {
 
 //Provides: caml_binaryen_expression_print
 //Requires: Binaryen
+//Requires: caml_sys_fds
 //Requires: caml_string_of_jsstring
 //Requires: caml_ml_output, caml_ml_string_length
 function caml_binaryen_expression_print(expr) {
   var text = Binaryen.emitText(expr);
-  var chanid = 1; // stdout
+  var chanid = caml_sys_fds[1].chanid; // stdout
   var s = caml_string_of_jsstring(text);
   caml_ml_output(chanid, s, 0, caml_ml_string_length(s));
 }
diff --git a/src/module.js b/src/module.js
index 4c344679..dbe0492d 100644
--- a/src/module.js
+++ b/src/module.js
@@ -17,31 +17,34 @@ function caml_binaryen_module_parse(text) {
 }
 
 //Provides: caml_binaryen_module_print
+//Requires: caml_sys_fds
 //Requires: caml_string_of_jsstring
 //Requires: caml_ml_output, caml_ml_string_length
 function caml_binaryen_module_print(wasm_mod) {
   var text = wasm_mod.emitText();
-  var chanid = 1; // stdout
+  var chanid = caml_sys_fds[1].chanid; // stdout
   var s = caml_string_of_jsstring(text);
   caml_ml_output(chanid, s, 0, caml_ml_string_length(s));
 }
 
 //Provides: caml_binaryen_module_print_asmjs
+//Requires: caml_sys_fds
 //Requires: caml_string_of_jsstring
 //Requires: caml_ml_output, caml_ml_string_length
 function caml_binaryen_module_print_asmjs(wasm_mod) {
   var asm = wasm_mod.emitAsmjs();
-  var chanid = 1; // stdout
+  var chanid = caml_sys_fds[1].chanid; // stdout
   var s = caml_string_of_jsstring(asm);
   caml_ml_output(chanid, s, 0, caml_ml_string_length(s));
 }
 
 //Provides: caml_binaryen_module_print_stack_ir
+//Requires: caml_sys_fds
 //Requires: caml_string_of_jsstring, caml_js_from_bool
 //Requires: caml_ml_output, caml_ml_string_length
 function caml_binaryen_module_print_stack_ir(wasm_mod, optimize) {
   var stackir = wasm_mod.emitStackIR(caml_js_from_bool(optimize));
-  var chanid = 1; // stdout
+  var chanid = caml_sys_fds[1].chanid; // stdout
   var s = caml_string_of_jsstring(stackir);
   caml_ml_output(chanid, s, 0, caml_ml_string_length(s));
 }
diff --git a/test/dune b/test/dune
index e9f7192b..e391294b 100644
--- a/test/dune
+++ b/test/dune
@@ -4,8 +4,7 @@
  (modes exe js)
  (flags
   :standard
-  (:include ./config/ocamlopt_flags.sexp))
- (js_of_ocaml))
+  (:include ./config/ocamlopt_flags.sexp)))
 
 (rule
  (alias runtest)
diff --git a/test/test.ml b/test/test.ml
index 55e949e9..e0339e08 100644
--- a/test/test.ml
+++ b/test/test.ml
@@ -82,7 +82,7 @@ let add =
 let _ = assert (Expression.Block.get_name add = Some "add")
 
 (* Create the add function *)
-let adder = Function.add_function wasm_mod "adder" (params ()) results [||] add
+let _adder = Function.add_function wasm_mod "adder" (params ()) results [||] add
 
 let call_adder =
   Expression.Call_indirect.make wasm_mod "table"