diff --git a/builder-web.opam b/builder-web.opam
index 4b001cb..e457876 100644
--- a/builder-web.opam
+++ b/builder-web.opam
@@ -46,7 +46,8 @@ depends: [
   "uri"
   "fmt" {>= "0.8.7"}
   "cmarkit" {>= "0.3.0"}
-  "tar" {< "3.0.0"}
+  "tar" {>= "3.0.0"}
+  "tar-unix" {>= "3.0.0"}
   "owee"
   "solo5-elftool" {>= "0.3.0"}
   "decompress" {>= "1.5.0"}
diff --git a/lib/builder_web.ml b/lib/builder_web.ml
index 54f78a4..588b03a 100644
--- a/lib/builder_web.ml
+++ b/lib/builder_web.ml
@@ -486,7 +486,13 @@ let routes ~datadir ~cachedir ~configdir ~expired_jobs =
     |> Option.to_result ~none:(`Msg "bad finish time") |> Result.map Int64.of_int
     |> Lwt.return |> if_error "Internal server error" >>= fun finish ->
     Dream.stream ~headers:["Content-Type", "application/tar+gzip"]
-      (Dream_tar.targz_response datadir finish artifacts)
+      (fun stream ->
+         let+ r = Dream_tar.targz_response datadir finish artifacts stream in
+         match r with
+         | Ok () -> ()
+         | Error _ ->
+           Log.warn (fun m -> m "error assembling gzipped tar archive");
+           ())
     |> Lwt_result.ok
   in
 
diff --git a/lib/dream_tar.ml b/lib/dream_tar.ml
index 2cad5f6..ef11a34 100644
--- a/lib/dream_tar.ml
+++ b/lib/dream_tar.ml
@@ -1,47 +1,36 @@
-open Lwt.Infix
+module High : sig
+  type t
+  type 'a s = 'a Lwt.t
 
-module Writer = struct
-  type out_channel =
-    { mutable gz : Gz.Def.encoder
-    ; ic : Cstruct.t
-    ; oc : Cstruct.t
-    ; stream : Dream.stream }
+  external inj : 'a s -> ('a, t) Tar.io = "%identity"
+  external prj : ('a, t) Tar.io -> 'a s = "%identity"
+end = struct
+  type t
+  type 'a s = 'a Lwt.t
 
-  type 'a t = 'a Lwt.t
-
-  let really_write ({ oc; stream; _ } as state) cs =
-    let rec until_await gz =
-      match Gz.Def.encode gz with
-      | `Await gz -> state.gz <- gz ; Lwt.return_unit
-      | `Flush gz ->
-        let max = Cstruct.length oc - Gz.Def.dst_rem gz in
-        let str = Cstruct.to_string ~len:max oc in
-        Dream.write stream str >>= fun () ->
-        let { Cstruct.buffer; off= cs_off; len= cs_len; } = oc in
-        until_await (Gz.Def.dst gz buffer cs_off cs_len)
-      | `End _gz -> assert false in
-    if Cstruct.length cs = 0
-    then Lwt.return_unit
-    else ( let { Cstruct.buffer; off; len; } = cs in
-           let gz = Gz.Def.src state.gz buffer off len in
-           until_await gz )
+  external inj : 'a -> 'b = "%identity"
+  external prj : 'a -> 'b = "%identity"
 end
 
-module HW = Tar.HeaderWriter(Lwt)(Writer)
+let value v = Tar.High (High.inj v)
 
-let write_block (header : Tar.Header.t) lpath ({ Writer.ic= buf; _ } as state) =
-  HW.write ~level:Tar.Header.Ustar header state >>= fun () ->
-  Lwt_io.open_file ~mode:Lwt_io.Input (Fpath.to_string lpath) >>= fun ic ->
-  let rec loop () =
-    let { Cstruct.buffer; off; len; } = buf in
-    Lwt_io.read_into_bigstring ic buffer off len >>= function
-    | 0 -> Lwt.return ()
-    | len' ->
-      Writer.really_write state (Cstruct.sub buf 0 len') >>= fun () ->
-      loop ()
+let ok_value v = value (Lwt_result.ok v)
+
+let run t stream =
+  let rec run : type a. (a, 'err, High.t) Tar.t -> (a, 'err) result Lwt.t =
+    function
+    | Tar.Write str ->
+      (* Can this not fail?!? Obviously, it can, but we never know?? *)
+      Lwt_result.ok (Dream.write stream str)
+    | Tar.Seek _ | Tar.Read _ | Tar.Really_read _ -> assert false
+    | Tar.Return value -> Lwt.return value
+    | Tar.High value -> High.prj value
+    | Tar.Bind (x, f) ->
+      let open Lwt_result.Syntax in
+      let* v = run x in
+      run (f v)
   in
-  loop () >>= fun () ->
-  Writer.really_write state (Tar.Header.zero_padding header)
+  run t
 
 let header_of_file mod_time (file : Builder_db.file) =
   let file_mode = if Fpath.is_prefix Fpath.(v "bin/") file.filepath then
@@ -51,38 +40,53 @@ let header_of_file mod_time (file : Builder_db.file) =
   in
   Tar.Header.make ~file_mode ~mod_time (Fpath.to_string file.filepath) (Int64.of_int file.size)
 
-let targz_response datadir finish (files : Builder_db.file list) (stream : Dream.stream) =
-  let state =
-    let ic = Cstruct.create (4 * 4 * 1024) in
-    let oc = Cstruct.create 4096 in
-    let gz =
-      let w = De.Lz77.make_window ~bits:15 in
-      let q = De.Queue.create 0x1000 in
-      let mtime = Int32.of_float (Unix.gettimeofday ()) in
-      let gz = Gz.Def.encoder `Manual `Manual ~mtime Gz.Unix ~q ~w ~level:4 in
-      let { Cstruct.buffer; off; len; } = oc in
-      Gz.Def.dst gz buffer off len
+let contents datadir file : unit -> (string option, _, _) Tar.t =
+  let state = ref `Initial in
+  let dispenser () =
+    let ( let* ) = Tar.( let* ) in
+    let src = Fpath.append datadir (Model.artifact_path file) in
+    let* state' =
+      match !state with
+      | `Initial ->
+        let* fd = ok_value (Lwt_io.open_file ~mode:Lwt_io.Input (Fpath.to_string src)) in
+        let s = `Active fd in
+        state := s; Tar.return (Ok s)
+      | `Active _ | `Closed as s -> Tar.return (Ok s)
     in
-    { Writer.gz; ic; oc; stream; }
+    match state' with
+    | `Closed -> Tar.return (Ok None)
+    | `Active fd ->
+      let* data = ok_value (Lwt_io.read ~count:65536 fd) in
+      if String.length data = 0 then begin
+        state := `Closed;
+        let* () = ok_value (Lwt_io.close fd) in
+        Tar.return (Ok None)
+      end else
+        Tar.return (Ok (Some data))
   in
-  Lwt_list.iter_s (fun file ->
-      let hdr = header_of_file finish file in
-      write_block hdr Fpath.(datadir // Model.artifact_path file) state)
-    files >>= fun () ->
-  Writer.really_write state Tar.Header.zero_block >>= fun () ->
-  Writer.really_write state Tar.Header.zero_block >>= fun () ->
-  (* assert (Gz.Def.encode gz = `Await) *)
-  let rec until_end gz = match Gz.Def.encode gz with
-    | `Await _gz -> assert false
-    | `Flush gz | `End gz as flush_or_end ->
-      let max = Cstruct.length state.oc - Gz.Def.dst_rem gz in
-      let str = Cstruct.to_string ~len:max state.oc in
-      Dream.write stream str >>= fun () -> match flush_or_end with
-      | `Flush gz ->
-        let { Cstruct.buffer; off= cs_off; len= cs_len; } = state.oc in
-        until_end (Gz.Def.dst gz buffer cs_off cs_len)
-      | `End _ -> Lwt.return_unit
+  dispenser
+
+let entries datadir finish files =
+  let files =
+    List.map (fun file ->
+        let hdr = header_of_file finish file in
+        let level = Some Tar.Header.Posix in
+        (level, hdr, contents datadir file)
+      )
+      files
   in
-  until_end (Gz.Def.src state.gz De.bigstring_empty 0 0) >>= fun () ->
-  Dream.flush stream >>= fun () ->
-  Dream.close stream
+  let files = ref files in
+  fun () -> match !files with
+    | [] -> Tar.return (Ok None)
+    | f :: fs -> files := fs; Tar.return (Ok (Some f))
+
+let targz_response datadir finish files stream =
+  let entries : (_, _) Tar.entries = entries datadir finish files in
+  let global_hdr =
+    Tar.Header.Extended.make
+      ~comment:"Tar file produced by builder-web.%%VERSION_NUM%%"
+      ()
+  in
+  let finish32 = Int64.to_int32 finish in
+  Logs.err (fun m -> m "finished at %ld (%Ld)" finish32 finish);
+  run (Tar_gz.out_gzipped ~level:9 ~mtime:finish32 Gz.Unix (Tar.out ~global_hdr entries)) stream
diff --git a/lib/dune b/lib/dune
index dd075a5..339158a 100644
--- a/lib/dune
+++ b/lib/dune
@@ -1,5 +1,5 @@
 (library
  (name builder_web)
  (libraries builder builder_db dream tyxml bos duration hex caqti-lwt
-   opamdiff ptime.clock.os cmarkit tar owee solo5-elftool decompress.de
+   opamdiff ptime.clock.os cmarkit tar tar.gz tar-unix owee solo5-elftool decompress.de
    decompress.gz uri))