diff --git a/boot/libs.ml b/boot/libs.ml
index 9e03f1aa4bde..51dd96685f70 100644
--- a/boot/libs.ml
+++ b/boot/libs.ml
@@ -1,6 +1,6 @@
 let executables = [ "main" ]
 
-let external_libraries = [ "unix"; "threads" ]
+let external_libraries = [ "unix"; "threads.posix"; "threads" ]
 
 let local_libraries =
   [ ("otherlibs/ordering", Some "Ordering", false, None)
diff --git a/src/dune_rules/dune_rules.ml b/src/dune_rules/dune_rules.ml
index a3a8ff2a4a0b..1f980da9e4b7 100644
--- a/src/dune_rules/dune_rules.ml
+++ b/src/dune_rules/dune_rules.ml
@@ -17,6 +17,7 @@ module Modules = Modules
 module Module_compilation = Module_compilation
 module Exe_rules = Exe_rules
 module Lib_rules = Lib_rules
+module Jsoo_rules = Jsoo_rules
 module Obj_dir = Obj_dir
 module Merlin_ident = Merlin_ident
 module Merlin = Merlin
diff --git a/src/dune_rules/jsoo_rules.ml b/src/dune_rules/jsoo_rules.ml
index 7cf8b4dfd90e..1ad640373e31 100644
--- a/src/dune_rules/jsoo_rules.ml
+++ b/src/dune_rules/jsoo_rules.ml
@@ -75,36 +75,17 @@ end
 module Version = struct
   type t = int list
 
-  let split_char ~sep p =
-    let len = String.length p in
-    let rec split beg cur =
-      if cur >= len then
-        if cur - beg > 0 then [ String.sub p ~pos:beg ~len:(cur - beg) ] else []
-      else if sep p.[cur] then
-        String.sub p ~pos:beg ~len:(cur - beg) :: split (cur + 1) (cur + 1)
-      else split beg (cur + 1)
-    in
-    split 0 0
-
-  let split v =
-    match
-      split_char
-        ~sep:(function
+  let of_string s : t =
+    let s =
+      match
+        String.findi s ~f:(function
           | '+' | '-' | '~' -> true
           | _ -> false)
-        v
-    with
-    | [] -> assert false
-    | x :: _ ->
-      List.map
-        (split_char
-           ~sep:(function
-             | '.' -> true
-             | _ -> false)
-           x)
-        ~f:int_of_string
-
-  let of_string : string -> t = split
+      with
+      | None -> s
+      | Some i -> String.take s i
+    in
+    String.split s ~on:'.' |> List.map ~f:int_of_string
 
   let rec compare v v' =
     match (v, v') with
@@ -122,7 +103,7 @@ module Version = struct
     let* _ = Build_system.build_file bin in
     Memo.of_reproducible_fiber
     @@ Process.run_capture_line Process.Strict bin [ "--version" ]
-    |> Memo.map ~f:of_string
+    |> Memo.map ~f:(fun s -> try Some (of_string s) with _ -> None)
 
   let version_memo =
     Memo.create "jsoo-version" ~input:(module Path) impl_version
@@ -327,9 +308,12 @@ let link_rule cc ~runtime ~target ~obj_dir cm ~flags ~linkall
              ; [ std_exit ]
              ])
       ; As
-          (match (Version.compare jsoo_verion [ 5; 1 ], linkall) with
-          | Lt, true | _, false -> []
-          | (Gt | Eq), true -> [ "--linkall" ])
+          (match (jsoo_verion, linkall) with
+          | Some version, true -> (
+            match Version.compare version [ 5; 1 ] with
+            | Lt -> []
+            | Gt | Eq -> [ "--linkall" ])
+          | None, _ | _, false -> [])
       ]
   in
   let spec = Command.Args.S [ Dep (Path.build runtime); Dyn get_all ] in
diff --git a/src/dune_rules/jsoo_rules.mli b/src/dune_rules/jsoo_rules.mli
index ab9042f242c8..c04beabe2b11 100644
--- a/src/dune_rules/jsoo_rules.mli
+++ b/src/dune_rules/jsoo_rules.mli
@@ -8,6 +8,14 @@ module Config : sig
   val all : t list
 end
 
+module Version : sig
+  type t = int list
+
+  val of_string : string -> t
+
+  val compare : t -> t -> Ordering.t
+end
+
 val build_cm :
      Super_context.t
   -> dir:Path.Build.t
diff --git a/test/expect-tests/jsoo_tests.ml b/test/expect-tests/jsoo_tests.ml
new file mode 100644
index 000000000000..aa43f5d5a23d
--- /dev/null
+++ b/test/expect-tests/jsoo_tests.ml
@@ -0,0 +1,45 @@
+open Stdune
+open Dune_rules
+open! Dune_engine
+open! Dune_tests_common
+
+let%expect_test _ =
+  let test s l =
+    let c = Jsoo_rules.Version.compare (Jsoo_rules.Version.of_string s) l in
+    let r =
+      match c with
+      | Eq -> "="
+      | Lt -> "<"
+      | Gt -> ">"
+    in
+    print_endline r
+  in
+  (* equal *)
+  test "5.0.1" [ 5; 0; 1 ];
+  [%expect {| = |}];
+  test "5.0.0" [ 5; 0 ];
+  [%expect {| = |}];
+  test "5.0" [ 5; 0; 0 ];
+  [%expect {| = |}];
+  test "5.0+1" [ 5; 0; 0 ];
+  [%expect {| = |}];
+  test "5.0~1" [ 5; 0; 0 ];
+  [%expect {| = |}];
+  test "5.0+1" [ 5; 0; 0 ];
+  [%expect {| = |}];
+  test "5.0.1+git-5.0.1-14-g904cf100b0" [ 5; 0; 1 ];
+  [%expect {| = |}];
+
+  test "5.0.1" [ 5; 0; 1; 1 ];
+  [%expect {| < |}];
+  test "5.0.1.1" [ 5; 0; 1 ];
+  [%expect {| > |}];
+  test "4.0.1" [ 5; 0; 1 ];
+  [%expect {| < |}];
+  test "5.0.1" [ 4; 0; 1 ];
+  [%expect {| > |}];
+  test "5.0.1" [ 5; 0 ];
+  [%expect {| > |}];
+  test "5.0" [ 5; 0; 1 ];
+  [%expect {| < |}];
+  ()