diff --git a/runtime/wasm/domain.wat b/runtime/wasm/domain.wat
index f5465bdf58..5ae970a00b 100644
--- a/runtime/wasm/domain.wat
+++ b/runtime/wasm/domain.wat
@@ -16,6 +16,12 @@
 ;; Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 
 (module
+   (import "obj" "caml_callback_1"
+      (func $caml_callback_1
+         (param (ref eq)) (param (ref eq)) (result (ref eq))))
+   (import "sync" "caml_ml_mutex_unlock"
+      (func $caml_ml_mutex_unlock (param (ref eq)) (result (ref eq))))
+
    (type $block (array (mut (ref eq))))
    (type $function_1 (func (param (ref eq) (ref eq)) (result (ref eq))))
    (type $closure (sub (struct (;(field i32);) (field (ref $function_1)))))
@@ -95,6 +101,47 @@
    (global $caml_domain_latest_id (export "caml_domain_latest_id") (mut i32)
       (i32.const 1))
 
+(@if (>= ocaml_version (5 2 0))
+(@then
+   (func (export "caml_domain_spawn")
+      (param $f (ref eq)) (param $term_sync_v (ref eq)) (result (ref eq))
+      (local $id i32) (local $old i32) (local $ts (ref $block)) (local $res (ref eq))
+      (local.set $id (global.get $caml_domain_latest_id))
+      (global.set $caml_domain_latest_id
+         (i32.add (local.get $id) (i32.const 1)))
+      (local.set $old (global.get $caml_domain_id))
+      (local.set $res
+         (call $caml_callback_1 (local.get $f) (ref.i31 (i32.const 0))))
+      (global.set $caml_domain_id (local.get $old))
+      (local.set $ts (ref.cast (ref $block) (local.get $term_sync_v)))
+      (drop (call $caml_ml_mutex_unlock (array.get $block (local.get $ts) (i32.const 2))))
+      ;; TODO: fix exn case
+      (array.set
+         $block
+         (local.get $ts)
+         (i32.const 1)
+         (array.new_fixed
+            $block
+            2
+            (ref.i31 (i32.const 0))
+            (array.new_fixed $block 2 (ref.i31 (i32.const 0)) (local.get $res))))
+      (ref.i31 (local.get $id)))
+)
+(@else
+   (func (export "caml_domain_spawn")
+      (param $f (ref eq)) (param $mutex (ref eq)) (result (ref eq))
+      (local $id i32) (local $old i32)
+      (local.set $id (global.get $caml_domain_latest_id))
+      (global.set $caml_domain_latest_id
+         (i32.add (local.get $id) (i32.const 1)))
+      (local.set $old (global.get $caml_domain_id))
+      (drop (call $caml_callback_1 (local.get $f) (ref.i31 (i32.const 0))))
+      (global.set $caml_domain_id (local.get $old))
+      (drop (call $caml_ml_mutex_unlock (local.get $mutex)))
+      (ref.i31 (local.get $id)))
+))
+
+
    (func (export "caml_ml_domain_id") (export "caml_ml_domain_index")
       (param (ref eq)) (result (ref eq))
       (ref.i31 (global.get $caml_domain_id)))
diff --git a/runtime/wasm/dune b/runtime/wasm/dune
index 84618077d7..c55cb470cd 100644
--- a/runtime/wasm/dune
+++ b/runtime/wasm/dune
@@ -3,32 +3,6 @@
  (package wasm_of_ocaml-compiler)
  (files runtime.wasm runtime.js))
 
-(rule
- (target version-dependent.wat)
- (deps version-dependent/post-5.2.wat)
- (enabled_if
-  (>= %{ocaml_version} 5.2.0))
- (action
-  (copy %{deps} %{target})))
-
-(rule
- (target version-dependent.wat)
- (deps version-dependent/post-5.1.wat)
- (enabled_if
-  (and
-   (>= %{ocaml_version} 5.1.0)
-   (< %{ocaml_version} 5.2.0)))
- (action
-  (copy %{deps} %{target})))
-
-(rule
- (target version-dependent.wat)
- (deps version-dependent/pre-5.1.wat)
- (enabled_if
-  (< %{ocaml_version} 5.1.0))
- (action
-  (copy %{deps} %{target})))
-
 (rule
  (target runtime.wasm)
  (deps
diff --git a/runtime/wasm/marshal.wat b/runtime/wasm/marshal.wat
index 246d41d356..389e97a31e 100644
--- a/runtime/wasm/marshal.wat
+++ b/runtime/wasm/marshal.wat
@@ -50,8 +50,6 @@
    (import "custom" "caml_find_custom_operations"
       (func $caml_find_custom_operations
          (param (ref $string)) (result (ref null $custom_operations))))
-   (import "version-dependent" "caml_marshal_header_size"
-      (global $caml_marshal_header_size i32))
 
    (global $input_val_from_string (ref $string)
       (array.new_fixed $string 21
@@ -723,6 +721,16 @@
 
    (data $marshal_data_size "Marshal.data_size")
 
+(@if (>= ocaml_version (5 1 0))
+(@then
+   (global $caml_marshal_header_size (export "caml_marshal_header_size") i32
+      (i32.const 16))
+)
+(@else
+   (global $caml_marshal_header_size (export "caml_marshal_header_size") i32
+      (i32.const 20))
+))
+
    (func (export "caml_marshal_data_size")
       (param $buf (ref eq)) (param $ofs (ref eq)) (result (ref eq))
       (local $s (ref $intern_state))
diff --git a/runtime/wasm/runtime_events.wat b/runtime/wasm/runtime_events.wat
index 9ac0f5f2f9..9c7efa6b01 100644
--- a/runtime/wasm/runtime_events.wat
+++ b/runtime/wasm/runtime_events.wat
@@ -33,6 +33,18 @@
          (local.get $evtag)
          (local.get $evtype)))
 
+(@if (>= ocaml_version (5 2 0))
+(@then
+   (func (export "caml_runtime_events_user_write")
+      (param (ref eq)) (param (ref eq)) (param (ref eq)) (result (ref eq))
+      (ref.i31 (i32.const 0)))
+)
+(@else
+   (func (export "caml_runtime_events_user_write")
+      (param (ref eq)) (param (ref eq)) (result (ref eq))
+      (ref.i31 (i32.const 0)))
+))
+
    (func (export "caml_runtime_events_user_resolve")
       (param (ref eq)) (param (ref eq)) (param (ref eq)) (result (ref eq))
       (ref.i31 (i32.const 0)))
diff --git a/runtime/wasm/version-dependent/post-5.1.wat b/runtime/wasm/version-dependent/post-5.1.wat
deleted file mode 100644
index 258505a5e9..0000000000
--- a/runtime/wasm/version-dependent/post-5.1.wat
+++ /dev/null
@@ -1,46 +0,0 @@
-;; Wasm_of_ocaml runtime support
-;; http://www.ocsigen.org/js_of_ocaml/
-;;
-;; This program is free software; you can redistribute it and/or modify
-;; it under the terms of the GNU Lesser General Public License as published by
-;; the Free Software Foundation, with linking exception;
-;; either version 2.1 of the License, or (at your option) any later version.
-;;
-;; This program is distributed in the hope that it will be useful,
-;; but WITHOUT ANY WARRANTY; without even the implied warranty of
-;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-;; GNU Lesser General Public License for more details.
-;;
-;; You should have received a copy of the GNU Lesser General Public License
-;; along with this program; if not, write to the Free Software
-;; Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
-
-(module
-   (import "obj" "caml_callback_1"
-      (func $caml_callback_1
-         (param (ref eq)) (param (ref eq)) (result (ref eq))))
-   (import "sync" "caml_ml_mutex_unlock"
-      (func $caml_ml_mutex_unlock (param (ref eq)) (result (ref eq))))
-   (import "domain" "caml_domain_latest_id"
-     (global $caml_domain_latest_id (mut i32)))
-   (import "domain" "caml_domain_id"
-     (global $caml_domain_id (mut i32)))
-
-   (func (export "caml_runtime_events_user_write")
-      (param (ref eq)) (param (ref eq)) (result (ref eq))
-      (ref.i31 (i32.const 0)))
-
-   (func (export "caml_domain_spawn")
-      (param $f (ref eq)) (param $mutex (ref eq)) (result (ref eq))
-      (local $id i32) (local $old i32)
-      (local.set $id (global.get $caml_domain_latest_id))
-      (global.set $caml_domain_latest_id
-         (i32.add (local.get $id) (i32.const 1)))
-      (local.set $old (global.get $caml_domain_id))
-      (drop (call $caml_callback_1 (local.get $f) (ref.i31 (i32.const 0))))
-      (global.set $caml_domain_id (local.get $old))
-      (drop (call $caml_ml_mutex_unlock (local.get $mutex)))
-      (ref.i31 (local.get $id)))
-
-   (global (export "caml_marshal_header_size") i32 (i32.const 16))
-)
diff --git a/runtime/wasm/version-dependent/post-5.2.wat b/runtime/wasm/version-dependent/post-5.2.wat
deleted file mode 100644
index b4183d2dcb..0000000000
--- a/runtime/wasm/version-dependent/post-5.2.wat
+++ /dev/null
@@ -1,59 +0,0 @@
-;; Wasm_of_ocaml runtime support
-;; http://www.ocsigen.org/js_of_ocaml/
-;;
-;; This program is free software; you can redistribute it and/or modify
-;; it under the terms of the GNU Lesser General Public License as published by
-;; the Free Software Foundation, with linking exception;
-;; either version 2.1 of the License, or (at your option) any later version.
-;;
-;; This program is distributed in the hope that it will be useful,
-;; but WITHOUT ANY WARRANTY; without even the implied warranty of
-;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-;; GNU Lesser General Public License for more details.
-;;
-;; You should have received a copy of the GNU Lesser General Public License
-;; along with this program; if not, write to the Free Software
-;; Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
-
-(module
-   (type $block (array (mut (ref eq))))
-   (import "obj" "caml_callback_1"
-      (func $caml_callback_1
-         (param (ref eq)) (param (ref eq)) (result (ref eq))))
-   (import "sync" "caml_ml_mutex_unlock"
-      (func $caml_ml_mutex_unlock (param (ref eq)) (result (ref eq))))
-   (import "domain" "caml_domain_latest_id"
-     (global $caml_domain_latest_id (mut i32)))
-   (import "domain" "caml_domain_id"
-     (global $caml_domain_id (mut i32)))
-
-   (func (export "caml_runtime_events_user_write")
-      (param (ref eq)) (param (ref eq)) (param (ref eq)) (result (ref eq))
-      (ref.i31 (i32.const 0)))
-
-   (func (export "caml_domain_spawn")
-      (param $f (ref eq)) (param $term_sync_v (ref eq)) (result (ref eq))
-      (local $id i32) (local $old i32) (local $ts (ref $block)) (local $res (ref eq))
-      (local.set $id (global.get $caml_domain_latest_id))
-      (global.set $caml_domain_latest_id
-         (i32.add (local.get $id) (i32.const 1)))
-      (local.set $old (global.get $caml_domain_id))
-      (local.set $res
-         (call $caml_callback_1 (local.get $f) (ref.i31 (i32.const 0))))
-      (global.set $caml_domain_id (local.get $old))
-      (local.set $ts (ref.cast (ref $block) (local.get $term_sync_v)))
-      (drop (call $caml_ml_mutex_unlock (array.get $block (local.get $ts) (i32.const 2))))
-      ;; TODO: fix exn case
-      (array.set
-         $block
-         (local.get $ts)
-         (i32.const 1)
-         (array.new_fixed
-            $block
-            2
-            (ref.i31 (i32.const 0))
-            (array.new_fixed $block 2 (ref.i31 (i32.const 0)) (local.get $res))))
-      (ref.i31 (local.get $id)))
-
-   (global (export "caml_marshal_header_size") i32 (i32.const 16))
-)
diff --git a/runtime/wasm/version-dependent/pre-5.1.wat b/runtime/wasm/version-dependent/pre-5.1.wat
deleted file mode 100644
index cc23b90ad7..0000000000
--- a/runtime/wasm/version-dependent/pre-5.1.wat
+++ /dev/null
@@ -1,46 +0,0 @@
-;; Wasm_of_ocaml runtime support
-;; http://www.ocsigen.org/js_of_ocaml/
-;;
-;; This program is free software; you can redistribute it and/or modify
-;; it under the terms of the GNU Lesser General Public License as published by
-;; the Free Software Foundation, with linking exception;
-;; either version 2.1 of the License, or (at your option) any later version.
-;;
-;; This program is distributed in the hope that it will be useful,
-;; but WITHOUT ANY WARRANTY; without even the implied warranty of
-;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-;; GNU Lesser General Public License for more details.
-;;
-;; You should have received a copy of the GNU Lesser General Public License
-;; along with this program; if not, write to the Free Software
-;; Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
-
-(module
-   (import "obj" "caml_callback_1"
-      (func $caml_callback_1
-         (param (ref eq)) (param (ref eq)) (result (ref eq))))
-   (import "sync" "caml_ml_mutex_unlock"
-      (func $caml_ml_mutex_unlock (param (ref eq)) (result (ref eq))))
-   (import "domain" "caml_domain_latest_id"
-     (global $caml_domain_latest_id (mut i32)))
-   (import "domain" "caml_domain_id"
-     (global $caml_domain_id (mut i32)))
-
-   (func (export "caml_runtime_events_user_write")
-      (param (ref eq)) (param (ref eq)) (result (ref eq))
-      (ref.i31 (i32.const 0)))
-
-   (func (export "caml_domain_spawn")
-      (param $f (ref eq)) (param $mutex (ref eq)) (result (ref eq))
-      (local $id i32) (local $old i32)
-      (local.set $id (global.get $caml_domain_latest_id))
-      (global.set $caml_domain_latest_id
-         (i32.add (local.get $id) (i32.const 1)))
-      (local.set $old (global.get $caml_domain_id))
-      (drop (call $caml_callback_1 (local.get $f) (ref.i31 (i32.const 0))))
-      (global.set $caml_domain_id (local.get $old))
-      (drop (call $caml_ml_mutex_unlock (local.get $mutex)))
-      (ref.i31 (local.get $id)))
-
-   (global (export "caml_marshal_header_size") i32 (i32.const 20))
-)