diff --git a/src/dune_file_watcher/dune_file_watcher.ml b/src/dune_file_watcher/dune_file_watcher.ml
index eaca7414a74f..e91f18c275f0 100644
--- a/src/dune_file_watcher/dune_file_watcher.ml
+++ b/src/dune_file_watcher/dune_file_watcher.ml
@@ -210,7 +210,7 @@ let shutdown t =
         Fsevents.stop fsevents.sync;
         Watch_trie.to_list fsevents.external_
         |> List.iter ~f:(fun (_, fs) -> Fsevents.stop fs))
-  | Fswatch_win _t -> `Thunk (fun () -> ())
+  | Fswatch_win _t -> `Thunk (fun () -> ()) (* TODO: clean up resources. *)
 
 let buffer_capacity = 65536
 
@@ -655,6 +655,21 @@ let wait_for_initial_watches_established_blocking t =
        before file access *)
     ()
 
+(* Return the parent directory of [ext] if [ext] denotes a file. *)
+let parent_directory ext =
+  let rec loop p =
+    if Path.is_directory (Path.external_ p) then Some ext
+    else
+      match Path.External.parent p with
+      | None ->
+        User_warning.emit
+          [ Pp.textf "Refusing to watch %s" (Path.External.to_string ext)
+          ];
+        None
+      | Some ext -> loop ext
+  in
+  loop ext
+
 let add_watch t path =
   match t.kind with
   | Fsevents f -> (
@@ -663,21 +678,7 @@ let add_watch t path =
     | In_build_dir _ ->
       Code_error.raise "attempted to watch a directory in build" []
     | External ext -> (
-      let ext =
-        let rec loop p =
-          if Path.is_directory (Path.external_ p) then Some ext
-          else
-            match Path.External.parent p with
-            | None ->
-              User_warning.emit
-                [ Pp.textf "Refusing to watch %s" (Path.External.to_string ext)
-                ];
-              None
-            | Some ext -> loop ext
-        in
-        loop ext
-      in
-      match ext with
+      match parent_directory ext with
       | None -> Ok ()
       | Some ext -> (
         let watch =
@@ -707,23 +708,12 @@ let add_watch t path =
       Code_error.raise "attempted to watch a directory in build" []
     | Path.In_source_tree _ -> Ok ()
     | External ext -> (
-      let ext =
-        let rec loop p =
-          if Path.is_directory (Path.external_ p) then Some ext
-          else
-            match Path.External.parent p with
-            | None ->
-              User_warning.emit
-                [ Pp.textf "Refusing to watch %s" (Path.External.to_string ext)
-                ];
-              None
-            | Some ext -> loop ext
-        in
-        loop ext
-      in
-      match ext with
+      match parent_directory ext with
       | None -> Ok ()
       | Some _ ->
+        (* TODO: here we can end up adding the same path multiple times.  We
+           should improve things to avoid doing this or to remove a child
+           directory when a parent directory is added. *)
         Fswatch_win.add fswatch.t (Path.to_absolute_filename path);
         Ok ()))