diff --git a/src/dune/lib_name.ml b/src/dune/lib_name.ml
index 9f19a41bc6fc..7687e05326b1 100644
--- a/src/dune/lib_name.ml
+++ b/src/dune/lib_name.ml
@@ -31,17 +31,15 @@ module Local = struct
       let hint_valid =
         Some
           (fun name ->
-            String.to_seq name
-            |> Seq.filter_map ~f:(fun c ->
-                   if valid_char c then
-                     Some c
-                   else
-                     match c with
-                     | '.'
-                     | '-' ->
-                       Some '_'
-                     | _ -> None)
-            |> String.of_seq)
+            String.filter_map name ~f:(fun c ->
+                if valid_char c then
+                  Some c
+                else
+                  match c with
+                  | '.'
+                  | '-' ->
+                    Some '_'
+                  | _ -> None))
 
       let of_string_opt (name : string) =
         match name with
diff --git a/src/dune/module_name.ml b/src/dune/module_name.ml
index 6376dff73d82..fda93d53a737 100644
--- a/src/dune/module_name.ml
+++ b/src/dune/module_name.ml
@@ -28,18 +28,15 @@ include Stringlike.Make (struct
   let hint_valid =
     Some
       (fun name ->
-        String.to_seq name
-        |> Seq.filter_map ~f:(fun c ->
-               if valid_char c then
-                 Some c
-               else
-                 match c with
-                 | '.'
-                 | '-' ->
-                   Some '_'
-                 | _ -> None
-        )
-        |> String.of_seq)
+        String.filter_map name ~f:(fun c ->
+            if valid_char c then
+              Some c
+            else
+              match c with
+              | '.'
+              | '-' ->
+                Some '_'
+              | _ -> None))
 
   let is_valid_module_name name =
     match name with
diff --git a/src/stdune/string.ml b/src/stdune/string.ml
index f2b9fe6563a6..42a8da2243eb 100644
--- a/src/stdune/string.ml
+++ b/src/stdune/string.ml
@@ -305,3 +305,7 @@ let of_list chars =
   let s = Bytes.make (List.length chars) '0' in
   List.iteri chars ~f:(fun i c -> Bytes.set s i c);
   Bytes.to_string s
+
+let filter_map t ~f =
+  (* TODO more efficient implementation *)
+  to_seq t |> Seq.filter_map ~f |> of_seq
diff --git a/src/stdune/string.mli b/src/stdune/string.mli
index ab3ebfcbb1c7..429bf261377b 100644
--- a/src/stdune/string.mli
+++ b/src/stdune/string.mli
@@ -128,3 +128,5 @@ val need_quoting : string -> bool
 (** [quote_for_shell s] quotes [s] using [Filename.quote] if [need_quoting s] is
     [true] *)
 val quote_for_shell : string -> string
+
+val filter_map : string -> f:(char -> char option) -> string