diff --git a/Makefile b/Makefile
index 084d03f2..8cdfdc17 100644
--- a/Makefile
+++ b/Makefile
@@ -10,6 +10,10 @@ watch :
 test :
 	dune runtest --no-buffer --force
 
+.PHONY : test-watch
+test-watch :
+	dune runtest --no-buffer --force --watch
+
 .PHONY : examples
 examples :
 	dune build \
diff --git a/src/FS_event.mli b/src/FS_event.mli
index cf0a3ec8..c7c738c1 100644
--- a/src/FS_event.mli
+++ b/src/FS_event.mli
@@ -43,7 +43,7 @@ val start :
   ?recursive:bool ->
   t ->
   string ->
-  ((string * (Event.t list), Error.t) result -> unit) ->
+  ((string option * (Event.t list), Error.t) result -> unit) ->
     unit
 (** Starts the handle and watches the given path for changes.
 
diff --git a/src/c/helpers.c b/src/c/helpers.c
index 7fcd8b67..46d710ef 100644
--- a/src/c/helpers.c
+++ b/src/c/helpers.c
@@ -142,10 +142,14 @@ static void luv_fs_event_trampoline(
 {
     caml_acquire_runtime_system();
     CAMLparam0();
-    CAMLlocal1(callback);
+    CAMLlocal2(callback, option);
     GET_HANDLE_CALLBACK(LUV_GENERIC_CALLBACK);
+    if (filename == NULL)
+        option = Val_none;
+    else
+        option = caml_alloc_some(caml_copy_string(filename));
     caml_callback3(
-        callback, caml_copy_string(filename), Val_int(events), Val_int(status));
+        callback, option, Val_int(events), Val_int(status));
     CAMLdrop;
     caml_release_runtime_system();
 }
@@ -641,6 +645,22 @@ int luv_os_uname(char *buffer)
 
 
 
+// String conversion functions.
+
+size_t luv_utf16_length_as_wtf8(const char *utf16, ssize_t utf16_len)
+{
+    return uv_utf16_length_as_wtf8((const uint16_t*)utf16, utf16_len);
+}
+
+int luv_utf16_to_wtf8(
+    const char *utf16, ssize_t utf16_len, char **wtf8_ptr,
+    size_t *wtf8_len_ptr)
+{
+    uv_utf16_to_wtf8((const uint16_t*)utf16, utf16_len, wtf8_ptr, wtf8_len_ptr);
+}
+
+
+
 // Other helpers.
 
 char* luv_version_suffix()
diff --git a/src/c/helpers.h b/src/c/helpers.h
index f73e32fb..61fb1f1f 100644
--- a/src/c/helpers.h
+++ b/src/c/helpers.h
@@ -188,6 +188,20 @@ int luv_os_uname(char *buffer);
 
 
 
+// String conversion functions. These are wrapped because it is convenient to
+// use Ctypes to pass OCaml strings directly to C code, but the Ctypes type
+// combinator for that purpose only compiles against C arguments of types such
+// as char*, and not uint16_t*. So these helpers add the necessary casts to
+// satisfy Ctypes.
+
+size_t luv_utf16_length_as_wtf8(const char *utf16, ssize_t utf16_len);
+
+int luv_utf16_to_wtf8(
+    const char *utf16, ssize_t utf16_len, char **wtf8_ptr,
+    size_t *wtf8_len_ptr);
+
+
+
 // Miscellaneous helpers - other things that are easiest to do in C.
 
 // Ctypes.constant can't bind a char*, so we return it instead.
diff --git a/src/c/luv_c_function_descriptions.ml b/src/c/luv_c_function_descriptions.ml
index f01a9f97..c152e641 100644
--- a/src/c/luv_c_function_descriptions.ml
+++ b/src/c/luv_c_function_descriptions.ml
@@ -1913,4 +1913,31 @@ struct
       foreign "uv_metrics_info"
         (ptr Types.Loop.t @-> ptr Types.Metrics.t @-> returning int)
   end
+
+  module String_ =
+  struct
+    let utf16_length_as_wtf8 =
+      foreign "luv_utf16_length_as_wtf8"
+        (string @-> PosixTypes.ssize_t @-> returning size_t)
+
+    let utf16_to_wtf8 =
+      foreign "luv_utf16_to_wtf8"
+        (string @->
+         PosixTypes.ssize_t @->
+         ptr (ptr char) @->
+         ptr size_t @->
+          returning error_code)
+
+    let wtf8_length_as_utf16 =
+      foreign "uv_wtf8_length_as_utf16"
+        (string @-> returning PosixTypes.ssize_t)
+
+    let wtf8_to_utf16 =
+      foreign "uv_wtf8_to_utf16"
+        (string @-> ptr uint16_t @-> size_t @-> returning void)
+
+    let free =
+      foreign "free"
+        (ptr void @-> returning void)
+  end
 end
diff --git a/src/c/shims.h b/src/c/shims.h
index dc742127..0ccf8029 100644
--- a/src/c/shims.h
+++ b/src/c/shims.h
@@ -746,3 +746,27 @@
 
     #define UV_EUNATCH 0x7242424
 #endif
+
+#if UV_VERSION_MAJOR == 1 && UV_VERSION_MINOR < 47
+    size_t uv_utf16_length_as_wtf8(const uint16_t *utf16, ssize_t utf16_len)
+    {
+        return ENOSYS;
+    }
+
+    int uv_utf16_to_wtf8(
+        const uint16_t *utf16, ssize_t utf16_len, char **wtf8_ptr,
+        size_t *wtf8_len_ptr)
+    {
+        return ENOSYS;
+    }
+
+    ssize_t uv_wtf8_length_as_utf16(const char *wtf8)
+    {
+        return ENOSYS;
+    }
+
+    void uv_wtf8_to_utf16(const char *utf8, uint16_t *utf16, size_t utf16_len)
+    {
+        abort();
+    }
+#endif
diff --git a/src/c/vendor/configure/commit-hash b/src/c/vendor/configure/commit-hash
index 38d66713..8417f27b 100644
--- a/src/c/vendor/configure/commit-hash
+++ b/src/c/vendor/configure/commit-hash
@@ -1 +1 @@
-f0bb7e40f0508bedf6fad33769b3f87bb8aedfa6
+be6b81a352d17513c95be153afcb3148f1a451cd
diff --git a/src/c/vendor/configure/configure b/src/c/vendor/configure/configure
index 5c44ac37..517b0857 100755
--- a/src/c/vendor/configure/configure
+++ b/src/c/vendor/configure/configure
@@ -1,6 +1,6 @@
 #! /bin/sh
 # Guess values for system-dependent variables and create Makefiles.
-# Generated by GNU Autoconf 2.71 for libuv 1.46.0.
+# Generated by GNU Autoconf 2.71 for libuv 1.47.0.
 #
 # Report bugs to <https://github.com/libuv/libuv/issues>.
 #
@@ -618,8 +618,8 @@ MAKEFLAGS=
 # Identity of this package.
 PACKAGE_NAME='libuv'
 PACKAGE_TARNAME='libuv'
-PACKAGE_VERSION='1.46.0'
-PACKAGE_STRING='libuv 1.46.0'
+PACKAGE_VERSION='1.47.0'
+PACKAGE_STRING='libuv 1.47.0'
 PACKAGE_BUGREPORT='https://github.com/libuv/libuv/issues'
 PACKAGE_URL=''
 
@@ -1390,7 +1390,7 @@ if test "$ac_init_help" = "long"; then
   # Omit some internal or obsolete options to make the list less imposing.
   # This message is too long to be a string in the A/UX 3.1 sh.
   cat <<_ACEOF
-\`configure' configures libuv 1.46.0 to adapt to many kinds of systems.
+\`configure' configures libuv 1.47.0 to adapt to many kinds of systems.
 
 Usage: $0 [OPTION]... [VAR=VALUE]...
 
@@ -1461,7 +1461,7 @@ fi
 
 if test -n "$ac_init_help"; then
   case $ac_init_help in
-     short | recursive ) echo "Configuration of libuv 1.46.0:";;
+     short | recursive ) echo "Configuration of libuv 1.47.0:";;
    esac
   cat <<\_ACEOF
 
@@ -1576,7 +1576,7 @@ fi
 test -n "$ac_init_help" && exit $ac_status
 if $ac_init_version; then
   cat <<\_ACEOF
-libuv configure 1.46.0
+libuv configure 1.47.0
 generated by GNU Autoconf 2.71
 
 Copyright (C) 2021 Free Software Foundation, Inc.
@@ -1832,7 +1832,7 @@ cat >config.log <<_ACEOF
 This file contains any messages produced by compilers while
 running configure, to aid debugging if configure makes a mistake.
 
-It was created by libuv $as_me 1.46.0, which was
+It was created by libuv $as_me 1.47.0, which was
 generated by GNU Autoconf 2.71.  Invocation command line was
 
   $ $0$ac_configure_args_raw
@@ -3169,7 +3169,7 @@ fi
 
 # Define the identity of the package.
  PACKAGE='libuv'
- VERSION='1.46.0'
+ VERSION='1.47.0'
 
 
 printf "%s\n" "#define PACKAGE \"$PACKAGE\"" >>confdefs.h
@@ -15042,7 +15042,7 @@ fi
 
 case $host_os in
   mingw*)
-    LIBS="$LIBS -lws2_32 -lpsapi -liphlpapi -lshell32 -luserenv -luser32 -ldbghelp -lole32 -luuid"
+    LIBS="$LIBS -lws2_32 -lpsapi -liphlpapi -lshell32 -luserenv -luser32 -ldbghelp -lole32 -luuid -lshell32"
  ;;
 esac
 case $host_os in
@@ -15741,7 +15741,7 @@ cat >>$CONFIG_STATUS <<\_ACEOF || ac_write_fail=1
 # report actual input values of CONFIG_FILES etc. instead of their
 # values after options handling.
 ac_log="
-This file was extended by libuv $as_me 1.46.0, which was
+This file was extended by libuv $as_me 1.47.0, which was
 generated by GNU Autoconf 2.71.  Invocation command line was
 
   CONFIG_FILES    = $CONFIG_FILES
@@ -15804,7 +15804,7 @@ ac_cs_config_escaped=`printf "%s\n" "$ac_cs_config" | sed "s/^ //; s/'/'\\\\\\\\
 cat >>$CONFIG_STATUS <<_ACEOF || ac_write_fail=1
 ac_cs_config='$ac_cs_config_escaped'
 ac_cs_version="\\
-libuv config.status 1.46.0
+libuv config.status 1.47.0
 configured by $0, generated by GNU Autoconf 2.71,
   with options \\"\$ac_cs_config\\"
 
diff --git a/src/c/vendor/libuv b/src/c/vendor/libuv
index f0bb7e40..be6b81a3 160000
--- a/src/c/vendor/libuv
+++ b/src/c/vendor/libuv
@@ -1 +1 @@
-Subproject commit f0bb7e40f0508bedf6fad33769b3f87bb8aedfa6
+Subproject commit be6b81a352d17513c95be153afcb3148f1a451cd
diff --git a/src/feature/detect_features.ml b/src/feature/detect_features.ml
index f1a9c656..b21d6dfe 100644
--- a/src/feature/detect_features.ml
+++ b/src/feature/detect_features.ml
@@ -303,6 +303,7 @@ let () =
   needs 37 "udp_recvmmsg" "See {!Luv.UDP.init}.";
   needs 32 "udp_set_source_membership" "See {!Luv.UDP.set_source_membership}.";
   needs 39 "udp_using_recvmmsg" "See {!Luv.UDP.using_recvmmsg}.";
+  needs 47 "utf_16" "See {!Luv.String}.";
 
   let mli_channel = open_out mli in
   Buffer.contents mli_buffer |> output_string mli_channel;
diff --git a/src/index.mld b/src/index.mld
index 89c3c149..5ba1ba1b 100644
--- a/src/index.mld
+++ b/src/index.mld
@@ -92,5 +92,6 @@ presented in the user guide.
 - {!Luv.Prepare} — pre-I/O callbacks
 - {!Luv.Check} — post-I/O callbacks
 - {!Luv.Idle} — per-iteration callbacks
+- {!Luv.String} — UTF-16 manipulation for Windows
 - {!Luv.Version} — libuv version
 - {!Luv.Require} — feature checks
diff --git a/src/luv.ml b/src/luv.ml
index 6b6b139b..b4b261a2 100644
--- a/src/luv.ml
+++ b/src/luv.ml
@@ -64,5 +64,6 @@ module Env = Env
 module Time = Time
 module Random = Random
 module Metrics = Metrics
+module String = String_
 module Require = Require
 module Unix = Luv_unix
diff --git a/src/string_.ml b/src/string_.ml
new file mode 100644
index 00000000..2126b7bb
--- /dev/null
+++ b/src/string_.ml
@@ -0,0 +1,57 @@
+(* This file is part of Luv, released under the MIT license. See LICENSE.md for
+   details, or visit https://github.com/aantron/luv/blob/master/LICENSE.md. *)
+
+
+
+let utf16_length_as_wtf8 s =
+  let result =
+    C.Functions.String_.utf16_length_as_wtf8
+      s
+      (PosixTypes.Ssize.of_int (String.length s / 2))
+    |> Unsigned.Size_t.to_int
+   in
+   if result < 0 then
+     Printf.ksprintf
+       failwith "Luv internal error: utf16_length_as_wtf8 error code %i;%s"
+       result "\nCheck your libuv version; 1.47.0 or higher required.";
+   result
+
+let utf16_to_wtf8 s =
+  let wtf8 = Ctypes.(allocate (ptr char) (coerce (ptr void) (ptr char) null)) in
+  let wtf8_length = Ctypes.(allocate size_t) Unsigned.Size_t.zero in
+  let error_code =
+   C.Functions.String_.utf16_to_wtf8
+      s
+      (PosixTypes.Ssize.of_int (String.length s / 2))
+      wtf8
+      wtf8_length
+  in
+  if error_code <> 0 then
+    Printf.ksprintf
+      failwith "Luv internal error: utf16_to_wtf8 error code %i;%s" error_code
+      "\nCheck your libuv version; 1.47.0 or higher required.";
+  let wtf8 = Ctypes.(!@ wtf8) in
+  let wtf8_length = Ctypes.(!@ wtf8_length) |> Unsigned.Size_t.to_int in
+  let s = Ctypes.string_from_ptr wtf8 ~length:wtf8_length in
+  C.Functions.String_.free Ctypes.(coerce (ptr char) (ptr void) wtf8);
+  s
+
+let wtf8_length_as_utf16 s =
+  let result =
+    C.Functions.String_.wtf8_length_as_utf16 s
+    |> PosixTypes.Ssize.to_int
+   in
+   if result < 0 then
+     Printf.ksprintf
+       failwith "Luv internal error: wtf8_length_as_utf16 error code %i;%s"
+       result "\nCheck your libuv version; 1.47.0 or higher required.";
+   result
+
+let wtf8_to_utf16 s =
+  let utf16_length = wtf8_length_as_utf16 s in
+  let utf16 = Ctypes.(allocate_n uint16_t) ~count:utf16_length in
+  C.Functions.String_.wtf8_to_utf16
+    s utf16 (Unsigned.Size_t.of_int utf16_length);
+  utf16
+  |> Ctypes.(coerce (ptr uint16_t) (ptr char))
+  |> Ctypes.string_from_ptr ~length:((utf16_length - 1) * 2)
diff --git a/src/string_.mli b/src/string_.mli
new file mode 100644
index 00000000..f9d7988b
--- /dev/null
+++ b/src/string_.mli
@@ -0,0 +1,36 @@
+(* This file is part of Luv, released under the MIT license. See LICENSE.md for
+   details, or visit https://github.com/aantron/luv/blob/master/LICENSE.md. *)
+
+
+
+val utf16_length_as_wtf8 : string -> int
+(** Binds {{:https://docs.libuv.org/en/v1.x/misc.html#c.uv_utf16_length_as_wtf8}
+    [uv_utf16_length_as_wtf8]}.
+
+    Requires Luv 0.5.13 and libuv 1.47.0.
+
+    {{!Luv.Require} Feature check}: [Luv.Require.(has utf_16)] *)
+
+val utf16_to_wtf8 : string -> string
+(** Binds {{:https://docs.libuv.org/en/v1.x/misc.html#c.uv_utf16_to_wtf8}
+    [uv_utf16_to_wtf8]}.
+
+    Requires Luv 0.5.13 and libuv 1.47.0.
+
+    {{!Luv.Require} Feature check}: [Luv.Require.(has utf_16)] *)
+
+val wtf8_length_as_utf16 : string -> int
+(** Binds {{:https://docs.libuv.org/en/v1.x/misc.html#c.uv_wtf8_length_as_utf16}
+    [uv_wtf8_length_as_utf16]}.
+
+    Requires Luv 0.5.13 and libuv 1.47.0.
+
+    {{!Luv.Require} Feature check}: [Luv.Require.(has utf_16)] *)
+
+val wtf8_to_utf16 : string -> string
+(** Binds {{:https://docs.libuv.org/en/v1.x/misc.html#c.uv_wtf8_to_utf16}
+    [uv_wtf8_to_utf16]}.
+
+    Requires Luv 0.5.13 and libuv 1.47.0.
+
+    {{!Luv.Require} Feature check}: [Luv.Require.(has utf_16)] *)
diff --git a/test/string_.ml b/test/string_.ml
new file mode 100644
index 00000000..8d6993a7
--- /dev/null
+++ b/test/string_.ml
@@ -0,0 +1,28 @@
+(* This file is part of Luv, released under the MIT license. See LICENSE.md for
+   details, or visit https://github.com/aantron/luv/blob/master/LICENSE.md. *)
+
+
+
+let tests = [
+  "string", [
+    "utf16_length_as_wtf8", `Quick, begin fun () ->
+      Luv.String.utf16_length_as_wtf8 "f\x00\xBB\x03"
+      |> Alcotest.(check int) "length" 3
+    end;
+
+    "utf16_to_wtf8", `Quick, begin fun () ->
+      Luv.String.utf16_to_wtf8 "f\x00\xBB\x03"
+      |> Alcotest.(check string) "value" "fλ"
+    end;
+
+    "wtf8_length_as_utf16", `Quick, begin fun () ->
+      Luv.String.wtf8_length_as_utf16 "fλ"
+      |> Alcotest.(check int) "length" 3
+    end;
+
+    "wtf8_to_utf16", `Quick, begin fun () ->
+      Luv.String.wtf8_to_utf16 "fλ"
+      |> Alcotest.(check string) "value" "f\x00\xBB\x03"
+    end;
+  ]
+]
diff --git a/test/tester.ml b/test/tester.ml
index eb9cf66d..09bb394d 100644
--- a/test/tester.ml
+++ b/test/tester.ml
@@ -24,4 +24,5 @@ let () =
     DNS.tests;
     Thread_.tests;
     Misc.tests;
+    String_.tests;
   ])
diff --git a/test/version.ml b/test/version.ml
index fde18659..935ea4c2 100644
--- a/test/version.ml
+++ b/test/version.ml
@@ -9,7 +9,7 @@ let tests = [
       Alcotest.(check int) "number" 1 Luv.Version.major);
 
     "minor", `Quick, (fun () ->
-      Alcotest.(check int) "number" 46 Luv.Version.minor);
+      Alcotest.(check int) "number" 47 Luv.Version.minor);
 
     "patch", `Quick, (fun () ->
       Alcotest.(check int) "number" 0 Luv.Version.patch);
@@ -21,12 +21,12 @@ let tests = [
       Alcotest.(check string) "suffix" "" Luv.Version.suffix);
 
     "hex", `Quick, (fun () ->
-      Alcotest.(check int) "number" 0x012E00 Luv.Version.hex);
+      Alcotest.(check int) "number" 0x012F00 Luv.Version.hex);
 
     "version", `Quick, (fun () ->
-      Alcotest.(check int) "number" 0x012E00 (Luv.Version.version ()));
+      Alcotest.(check int) "number" 0x012F00 (Luv.Version.version ()));
 
     "string", `Quick, (fun () ->
-      Alcotest.(check string) "value" "1.46.0" (Luv.Version.string ()));
+      Alcotest.(check string) "value" "1.47.0" (Luv.Version.string ()));
   ]
 ]