diff --git a/server/backend/check.ml b/server/backend/check.ml
index 5fc1e27..17a8c56 100644
--- a/server/backend/check.ml
+++ b/server/backend/check.ml
@@ -140,51 +140,61 @@ let failure_kind logfile =
     lookup `Other
   end
 
-let with_test pkg = {|
+let with_test ~opam pkg =
+  fmt {|
 if [ $res = 0 ]; then
-    opam remove -y "|}^pkg^{|"
-    opam install -vty "|}^pkg^{|"
+    %s remove -y %s
+    %s install -vty %s
     res=$?
     if [ $res = 20 ]; then
         res=0
     fi
 fi
-|}
+|} opam pkg opam pkg
 
 let with_test ~conf pkg =
   if Server_configfile.with_test conf then
-    with_test pkg
+    let opam = match platform_os conf with `Windows -> "ocaml-env exec --64 -- opam" | _ -> "opam" in
+    with_test ~opam pkg
   else
     ""
 
-let with_lower_bound pkg = {|
+let with_lower_bound ~opam pkg =
+  fmt {|
 if [ $res = 0 ]; then
-    opam remove -y "|}^pkg^{|"
-    env OPAMCRITERIA="+removed,+count[version-lag,solution]" opam install -vy "|}^pkg^{|"
+    %s remove -y "%s"
+    env OPAMCRITERIA="+removed,+count[version-lag,solution]" opam install -vy "%s"
     res=$?
 fi
-|}
+|} opam pkg pkg
 
 let with_lower_bound ~conf pkg =
   if Server_configfile.with_lower_bound conf then
-    with_lower_bound pkg
+    let opam = match platform_os conf with `Windows -> "ocaml-env exec --64 -- opam" | _ -> "opam" in
+    with_lower_bound ~opam pkg
   else
     ""
 
-let run_script ~conf pkg = {|
-opam remove -y "|}^pkg^{|"
-opam install -vy "|}^pkg^{|"
+let run_script ~conf pkg =
+  let windows = match platform_os conf with `Windows -> true | _ -> false in
+  let opam = if windows then "ocaml-env exec --64 -- opam" else "opam" in
+  let platform_distribution = Server_configfile.platform_distribution conf in
+  let with_test = with_test ~conf pkg in
+  let with_lower_bound = with_lower_bound ~conf pkg in
+  fmt {|
+%s remove -y "%s"
+%s install -vy "%s"
 res=$?
 if [ $res = 31 ]; then
-    if opam show -f x-ci-accept-failures: "|}^pkg^{|" | grep -q '"|}^Server_configfile.platform_distribution conf^{|"'; then
+    if %s show -f x-ci-accept-failures: "%s" | grep -q '"%s"'; then
         echo "This package failed and has been disabled for CI using the 'x-ci-accept-failures' field."
         exit 69
     fi
 fi
-|}^with_test ~conf pkg^{|
-|}^with_lower_bound ~conf pkg^{|
+%s
+%s
 exit $res
-|}
+|} opam pkg opam pkg opam pkg platform_distribution with_test with_lower_bound
 
 let run_job ~cap ~conf ~pool ~stderr ~base_obuilder ~switch ~num logdir pkg =
   Lwt_pool.use pool begin fun () ->
@@ -232,19 +242,25 @@ let get_obuilder ~conf ~opam_repo ~opam_repo_commit ~extra_repos switch =
       | Some for_switches -> List.exists (Intf.Compiler.equal switch) for_switches
     ) extra_repos
   in
-  let open Obuilder_spec in
   let cache = cache ~conf in
-  let from = match Server_configfile.platform_os conf with
-    | "linux" -> Server_configfile.platform_image conf
-    | os -> failwith ("OS '"^os^"' not supported") (* TODO: Should other platforms simply take the same ocurrent/opam: prefix? *)
-  in
+  let network = network (platform_os conf) in
+  let from = Server_configfile.platform_image conf in
+  let windows = match platform_os conf with `Windows -> true | _ -> false in
+  let opam = if windows then "ocaml-env exec --64 -- opam" else "opam" in
+  let open Obuilder_spec in
   stage ~from begin
-    [ user ~uid:1000 ~gid:1000;
+    (if windows then
+       [ user_windows ~name:"ContainerAdministrator";
+         shell ["/cygwin64/bin/bash.exe"; "--login"; "-c"];
+         run "%s config set-global jobs $NUMBER_OF_PROCESSORS" opam; ]
+     else
+       [ user_unix ~uid:1000 ~gid:1000;
+         env "OPAMEXTERNALSOLVER" "builtin-0install";
+         run "sudo ln -f /usr/bin/opam-dev /usr/bin/opam"; ]
+    ) @ [
       env "OPAMPRECISETRACKING" "1"; (* NOTE: See https://github.com/ocaml/opam/issues/3997 *)
       env "OPAMUTF8" "never"; (* Disable UTF-8 characters so that output stay consistant accross platforms *)
-      env "OPAMEXTERNALSOLVER" "builtin-0install";
       env "OPAMCRITERIA" "+removed";
-      run "sudo ln -f /usr/bin/opam-dev /usr/bin/opam";
       run ~network "rm -rf ~/opam-repository && git clone -q '%s' ~/opam-repository && git -C ~/opam-repository checkout -q %s" (Intf.Github.url opam_repo) opam_repo_commit;
       run "rm -rf ~/.opam && opam init -ya --bare --config ~/.opamrc-sandbox ~/opam-repository";
     ] @
@@ -253,30 +269,36 @@ let get_obuilder ~conf ~opam_repo ~opam_repo_commit ~extra_repos switch =
         let name = Filename.quote (Intf.Repository.name repo) in
         let url = Intf.Github.url (Intf.Repository.github repo) in
         [ run ~network "git clone -q '%s' ~/%s && git -C ~/%s checkout -q %s" url name name hash;
-          run "opam repository add --dont-select %s ~/%s" name name;
+          run "%s repository add --dont-select %s ~/%s" opam name name;
         ]
       ) extra_repos
     ) @ [
-      run ~cache ~network "opam switch create --repositories=%sdefault '%s' '%s'"
+      run ~cache ~network "%s switch create --repositories=%sdefault '%s' '%s'"
+        opam
         (List.fold_left (fun acc (repo, _) -> Intf.Repository.name repo^","^acc) "" extra_repos)
         (Intf.Compiler.to_string (Intf.Switch.name switch))
         (Intf.Switch.switch switch);
-      run ~network "opam update --depexts";
-    ] @
-    (* TODO: Should this be removed now that it is part of the base docker images? What about macOS? *)
-    (if OpamVersionCompare.compare (Intf.Switch.switch switch) "4.08" < 0 then
-       [run ~cache ~network "opam install -y ocaml-secondary-compiler"]
-       (* NOTE: See https://github.com/ocaml/opam-repository/pull/15404
-                and https://github.com/ocaml/opam-repository/pull/15642 *)
-     else
-       []
+    ] @ (
+      if windows then
+        [ shell ["cmd"; "/S"; "/C"];
+          run ~network {|C:\cygwin-setup-x86_64.exe --quiet-mode --no-shortcuts --no-startmenu --no-desktop --only-site --local-package-dir C:\TEMP\cache --root=C:\cygwin64 --site https://mirrors.kernel.org/sourceware/cygwin/ --upgrade-also|};
+          shell ["/cygwin64/bin/bash.exe"; "--login"; "-c"]; ]
+      else
+        ([ run ~network "opam update --depexts"; ]
+        (* TODO: Should this be removed now that it is part of the base docker images? What about macOS? *)
+        @ (if OpamVersionCompare.compare (Intf.Switch.switch switch) "4.08" < 0 then
+             [run ~cache ~network "opam install -y ocaml-secondary-compiler"]
+           (* NOTE: See https://github.com/ocaml/opam-repository/pull/15404
+              and https://github.com/ocaml/opam-repository/pull/15642 *)
+           else
+             []))
     ) @
     (match Server_configfile.extra_command conf with
      | Some c -> [run ~cache ~network "%s" c]
      | None -> []
     ) @
     (if Server_configfile.enable_dune_cache conf then
-       [ run ~cache ~network "opam pin add -k version dune $(opam show -f version dune)";
+       [ run ~cache ~network "%s pin add -k version dune $(opam show -f version dune)" opam;
          env "DUNE_CACHE" "enabled";
          env "DUNE_CACHE_TRANSPORT" "direct";
          env "DUNE_CACHE_DUPLICATION" "copy";
@@ -329,14 +351,16 @@ let with_stderr ~start_time workdir f =
 
 module Pkg_set = Set.Make (String)
 
-let revdeps_script pkg =
+let revdeps_script ~conf pkg =
+  let opam = match platform_os conf with `Windows -> "ocaml-env exec --64 -- opam" | _ -> "opam" in
   let pkg = Filename.quote pkg in
-  {|opam list --color=never -s --recursive --depopts --depends-on |}^pkg^{| && \
-    opam list --color=never -s --with-test --with-doc --depopts --depends-on |}^pkg
+  fmt {|%s list --color=never -s --recursive --depopts --depends-on %s && \
+        %s list --color=never -s --with-test --with-doc --depopts --depends-on %s|}
+    opam pkg opam pkg
 
 let get_metadata ~debug ~jobs ~cap ~conf ~pool ~stderr logdir (_, base_obuilder) pkgs =
   let get_revdeps ~base_obuilder ~pkgname ~pkg ~logdir =
-    let%lwt revdeps = ocluster_build_str ~important:false ~debug ~cap ~conf ~base_obuilder ~stderr ~default:(Some []) (revdeps_script pkg) in
+    let%lwt revdeps = ocluster_build_str ~important:false ~debug ~cap ~conf ~base_obuilder ~stderr ~default:(Some []) (revdeps_script ~conf pkg) in
     let module Set = Set.Make(String) in
     let revdeps = Set.of_list revdeps in
     let revdeps = Set.remove pkgname revdeps in (* https://github.com/ocaml/opam/issues/4446 *)
@@ -346,8 +370,9 @@ let get_metadata ~debug ~jobs ~cap ~conf ~pool ~stderr logdir (_, base_obuilder)
   in
   let get_latest_metadata ~base_obuilder ~pkgname ~logdir = (* TODO: Get this locally by merging all the repository and parsing the opam files using opam-core *)
     let%lwt opam =
+      let opam = match platform_os conf with `Windows -> "ocaml-env exec --64 -- opam" | _ -> "opam" in
       ocluster_build_str ~important:false ~debug ~cap ~conf ~base_obuilder ~stderr ~default:(Some [])
-        ("opam show --raw "^Filename.quote pkgname)
+        (opam ^ " show --raw " ^ Filename.quote pkgname)
     in
     Lwt_io.with_file ~mode:Lwt_io.output (Fpath.to_string (Server_workdirs.tmpopamfile ~pkg:pkgname logdir)) (fun c ->
       Lwt_io.write c (String.concat "\n" opam)