diff --git a/bin/forester/main.ml b/bin/forester/main.ml
index 41875fa..a741f31 100644
--- a/bin/forester/main.ml
+++ b/bin/forester/main.ml
@@ -139,41 +139,6 @@ let theme_dir ~(config : Config.t) =
       None
     end
 
-let mtime path = (EP.stat ~follow:true path).mtime
-
-let theme_dir_has_changed ~env ~(forest : State.t) theme_dir =
-  let rec dir_up_to_date src dst =
-    EP.is_directory dst
-    &&
-    let sorted = List.sort compare in
-    let src_entries = sorted (EP.read_dir src) in
-    let dst_entries = sorted (EP.read_dir dst) in
-    src_entries = dst_entries
-    && List.for_all
-         (fun name -> entry_up_to_date EP.(src / name) EP.(dst / name))
-         src_entries
-  and entry_up_to_date src dst =
-    if EP.is_directory src then dir_up_to_date src dst
-    else mtime src <= mtime dst
-  in
-  let visible_dir_entries dir =
-    List.filter
-      (fun name -> not (String.starts_with ~prefix:"." name))
-      (EP.read_dir dir)
-  in
-  try
-    let cwd = Eio.Stdenv.cwd env in
-    let src = EP.(env#fs / theme_dir) in
-    let dst = Forester.output_path ~cwd ~forest in
-    if
-      EP.is_directory dst
-      && List.for_all
-           (fun name -> entry_up_to_date EP.(src / name) EP.(dst / name))
-           (visible_dir_entries src)
-    then false
-    else true
-  with _ -> true
-
 let build ~env ~sw _ config_path dev no_theme emit_legacy_xml =
   match Config_parser.parse_forest_config_file ~env config_path with
   | Error errors -> List.iter Error.print_config_error errors
@@ -192,19 +157,22 @@ let build ~env ~sw _ config_path dev no_theme emit_legacy_xml =
           m "Build_forest: %.3fs" (Unix.gettimeofday () -. start));
       (forest, pending_jobs)
     in
-    if not no_theme then begin
-      let@ theme_dir = Option.iter @~ theme_dir ~config in
-      if theme_dir_has_changed ~env ~forest theme_dir then
-        begin match Eio_util.path_of_dir ~env theme_dir with
-        | Ok path -> Forester.copy_contents_of_dir ~env ~forest path
-        | Error exn -> Error.(print ~config @@ io_error exn)
-        end
-    end;
-    Forester.render_forest ~progress:render_progress ~forest ~emit_legacy_xml ();
+    let theme_copied =
+      if no_theme then None
+      else
+        Option.map
+          (fun theme_dir ->
+            let@ () = Eio.Fiber.fork_promise ~sw in
+            match Eio_util.path_of_dir ~env theme_dir with
+            | Ok path -> Forester.copy_contents_of_dir ~env ~forest path
+            | Error exn -> Error.(print ~config @@ io_error exn))
+          (theme_dir ~config)
+    in
     begin match Eio.Promise.await pending_jobs with
     | Ok () -> ()
     | Error exn -> raise exn
     end;
+    Forester.render_forest ~progress:render_progress ~forest ~emit_legacy_xml ();
     finalise_progress_display ();
     Link_checker.check_and_report_all ~forest;
     let elapsed = Unix.gettimeofday () -. start_time in
@@ -219,7 +187,8 @@ let build ~env ~sw _ config_path dev no_theme emit_legacy_xml =
     Logs.app (fun m ->
         m "Built %d tree%s%s in %.1fs" n_trees
           (if n_trees = 1 then "" else "s")
-          other_note elapsed)
+          other_note elapsed);
+    Option.iter Eio.Promise.await_exn theme_copied
 
 let new_tree ~env ~sw config_path dest_dir prefix template random =
   match Config_parser.parse_forest_config_file ~env config_path with
diff --git a/lib/compiler/Eio_util.ml b/lib/compiler/Eio_util.ml
index 2bbbc66..4583377 100644
--- a/lib/compiler/Eio_util.ml
+++ b/lib/compiler/Eio_util.ml
@@ -132,7 +132,7 @@ let copy_to_dir ~env ~cwd ~sources ~dest_dir =
     Path.mkdirs ~exists_ok:true ~perm:0o755 path;
     if Sys.unix then
       run_process ~quiet:true ~env ~cwd
-        (["cp"; "-r"; "-L"] @ sources @ [dest_dir])
+        (["cp"; "-R"; "-L"; "-f"] @ sources @ [dest_dir])
     else
       let@ source = List.iter @~ sources in
       run_process ~quiet:true ~env ~cwd ["xcopy"; source; dest_dir ^ "/"]