diff --git a/dune-project b/dune-project
index cbf2f44e..3340ac75 100644
--- a/dune-project
+++ b/dune-project
@@ -1,19 +1,16 @@
 (lang dune 2.7)
-
 (name obuilder)
 (formatting disabled)
-
 (generate_opam_files true)
-
 (source (github ocurrent/obuilder))
 (authors "talex5@gmail.com")
 (maintainers "talex5@gmail.com")
 (documentation "https://ocurrent.github.io/obuilder/")
-
 (package
  (name obuilder)
  (synopsis "Run build scripts for CI")
- (description "OBuilder takes a build script (similar to a Dockerfile) and performs the steps in it in a sandboxed environment.")
+ (description
+  "OBuilder takes a build script (similar to a Dockerfile) and performs the steps in it in a sandboxed environment.")
  (depends
   lwt
   astring
@@ -29,18 +26,16 @@
   sqlite3
   obuilder-spec
   (ocaml (>= 4.10.0))
-  (alcotest-lwt :with-test)
-))
-
+  (alcotest-lwt :with-test)))
 (package
  (name obuilder-spec)
  (synopsis "Build specification format")
- (description "A library for constructing, reading and writing OBuilder build specification files.")
+ (description
+  "A library for constructing, reading and writing OBuilder build specification files.")
  (depends
+  (fmt (>= 0.8.9))
   sexplib
   astring
   ppx_deriving
   ppx_sexp_conv
-  (dockerfile (>= 6.6.0))
-  (ocaml (>= 4.10.0))
-))
+  (ocaml (>= 4.10.0))))
diff --git a/lib_spec/docker.ml b/lib_spec/docker.ml
index acf14ac7..2122c2b2 100644
--- a/lib_spec/docker.ml
+++ b/lib_spec/docker.ml
@@ -1,5 +1,3 @@
-open Dockerfile
-
 type ctx = {
   user : Spec.user;
 }
@@ -12,49 +10,65 @@ let default_ctx = {
 let pp_pair f (k, v) =
   Fmt.pf f "%s=%s" k v
 
-let wrap x =
-  x
-  |> String.split_on_char '\n'
-  |> List.map String.trim
-  |> String.concat " \\\n    "
-
-let of_op ~buildkit (acc, ctx) : Spec.op -> Dockerfile.t list * ctx = function
-  | `Comment x -> comment "%s" x :: acc, ctx
-  | `Workdir x -> workdir "%s" x :: acc, ctx
-  | `Shell xs -> shell xs :: acc, ctx
-  | `Run { cache = (_ :: _) as cache; shell; network = _ } when buildkit ->
-    let mounts =
-      cache |> List.map (fun { Cache.id; target; buildkit_options } ->
-          let buildkit_options =
-            ("--mount=type", "cache") ::
-            ("id", id) ::
-            ("target", target) ::
-            ("uid", string_of_int ctx.user.uid) ::
-            buildkit_options
-          in
-          Fmt.strf "@[<h>%a@]" Fmt.(list ~sep:(unit ",") pp_pair) buildkit_options
-        )
-    in
-    run "%s %s" (String.concat " " mounts) (wrap shell) :: acc, ctx
-  | `Run { cache = _; network = _; shell } -> run "%s" (wrap shell) :: acc, ctx
-  | `Copy { from; src; dst; exclude = _ } ->
-    let from = match from with
-      | `Build name -> Some name
-      | `Context -> None
-    in
-    if ctx.user = Spec.root then copy ?from ~src ~dst () :: acc, ctx
+let pp_wrap =
+  Fmt.using (String.split_on_char '\n')
+    Fmt.(list ~sep:(unit " \\@\n    ") (using String.trim string))
+
+let pp_cache ~ctx f { Cache.id; target; buildkit_options } =
+  let buildkit_options =
+    ("--mount=type", "cache") ::
+    ("id", id) ::
+    ("target", target) ::
+    ("uid", string_of_int ctx.user.uid) ::
+    buildkit_options
+  in
+  Fmt.pf f "%a" Fmt.(list ~sep:(unit ",") pp_pair) buildkit_options
+
+let pp_run ~ctx f { Spec.cache; shell; network = _ } =
+  Fmt.pf f "RUN %a%a" Fmt.(list (pp_cache ~ctx ++ const string " ")) cache pp_wrap shell
+
+let pp_copy ~ctx f { Spec.from; src; dst; exclude = _ } =
+  let from = match from with
+    | `Build name -> Some name
+    | `Context -> None
+  in
+  let chown =
+    if ctx.user = Spec.root then None
     else (
       let { Spec.uid; gid } = ctx.user in
-      let chown = Printf.sprintf "%d:%d" uid gid in
-      copy ?from ~chown ~src ~dst () :: acc, ctx
+      Some (Printf.sprintf "%d:%d" uid gid)
     )
-  | `User ({ uid; gid } as u) -> user "%d:%d" uid gid :: acc, { user = u }
-  | `Env b -> env [b] :: acc, ctx
+  in
+  Fmt.pf f "COPY %a%a%a %s"
+    Fmt.(option (fmt "--chown=%s ")) chown
+    Fmt.(option (fmt "--from=%s ")) from
+    Fmt.(list ~sep:sp string) src
+    dst
+
+let pp_op ~buildkit ctx f : Spec.op -> ctx = function
+  | `Comment x                -> Fmt.pf f "# %s" x; ctx
+  | `Workdir x                -> Fmt.pf f "WORKDIR %s" x; ctx
+  | `Shell xs                 -> Fmt.pf f "SHELL [ %a ]" Fmt.(list ~sep:comma (quote string)) xs; ctx
+  | `Run x when buildkit      -> pp_run ~ctx f x; ctx
+  | `Run x                    -> pp_run ~ctx f { x with cache = [] }; ctx
+  | `Copy x                   -> pp_copy ~ctx f x; ctx
+  | `User ({ uid; gid } as u) -> Fmt.pf f "USER %d:%d" uid gid; { user = u }
+  | `Env (k, v)               -> Fmt.pf f "ENV %s %s" k v; ctx
 
-let rec convert ?name ~buildkit { Spec.child_builds; from; ops } =
-  let stages = child_builds |> List.map (fun (name, spec) -> convert ~name ~buildkit spec) |> List.flatten in
-  let ops', _ctx = List.fold_left (of_op ~buildkit) ([], default_ctx) ops in
-  stages @ [Dockerfile.from ?alias:name from @@@ List.rev ops']
+let rec convert ~buildkit f (name, { Spec.child_builds; from; ops }) =
+  child_builds |> List.iter (fun (name, spec) ->
+      convert ~buildkit f (Some name, spec);
+      Format.pp_print_newline f ();
+    );
+  Fmt.pf f "@[<h>FROM %s%a@]@." from Fmt.(option (const string " as " ++ string)) name;
+  let (_ : ctx) = List.fold_left (fun ctx op ->
+      Format.pp_open_hbox f ();
+      let ctx = pp_op ~buildkit ctx f op in
+      Format.pp_close_box f ();
+      Format.pp_print_newline f ();
+      ctx
+    ) default_ctx ops
+  in ()
 
 let dockerfile_of_spec ~buildkit t =
-  Dockerfile.empty @@@ convert ~buildkit t
+  Fmt.strf "%a" (convert ~buildkit) (None, t)
diff --git a/lib_spec/docker.mli b/lib_spec/docker.mli
index 572e8468..83fe91e4 100644
--- a/lib_spec/docker.mli
+++ b/lib_spec/docker.mli
@@ -1,4 +1,4 @@
-val dockerfile_of_spec : buildkit:bool -> Spec.t -> Dockerfile.t
+val dockerfile_of_spec : buildkit:bool -> Spec.t -> string
 (** [dockerfile_of_spec x] produces a Dockerfile that aims to be equivalent to [x].
 
     However, note that:
diff --git a/lib_spec/dune b/lib_spec/dune
index 3b746f43..d7ecfb47 100644
--- a/lib_spec/dune
+++ b/lib_spec/dune
@@ -2,4 +2,4 @@
   (name obuilder_spec)
   (public_name obuilder-spec)
   (preprocess (pps ppx_sexp_conv))
-  (libraries astring sexplib dockerfile))
+  (libraries astring sexplib fmt))
diff --git a/main.ml b/main.ml
index 60fb5b96..1d6b056b 100644
--- a/main.ml
+++ b/main.ml
@@ -59,7 +59,6 @@ let dockerfile buildkit spec =
   Sexplib.Sexp.load_sexp spec
   |> Obuilder_spec.t_of_sexp
   |> Obuilder_spec.Docker.dockerfile_of_spec ~buildkit
-  |> Dockerfile.string_of_t
   |> print_endline
 
 open Cmdliner
diff --git a/obuilder-spec.opam b/obuilder-spec.opam
index 6a966a51..aac0d75b 100644
--- a/obuilder-spec.opam
+++ b/obuilder-spec.opam
@@ -10,11 +10,11 @@ doc: "https://ocurrent.github.io/obuilder/"
 bug-reports: "https://github.com/ocurrent/obuilder/issues"
 depends: [
   "dune" {>= "2.7"}
+  "fmt" {>= "0.8.9"}
   "sexplib"
   "astring"
   "ppx_deriving"
   "ppx_sexp_conv"
-  "dockerfile" {>= "6.6.0"}
   "ocaml" {>= "4.10.0"}
   "odoc" {with-doc}
 ]
diff --git a/test/test.ml b/test/test.ml
index 749a9e6e..0558377d 100644
--- a/test/test.ml
+++ b/test/test.ml
@@ -429,14 +429,13 @@ let remove_line_indents = function
 let remove_indent s =
   String.split_on_char '\n' s
   |> remove_line_indents
-  |> List.filter ((<>) "")
   |> String.concat "\n"
 
 
 (* Check that parsing an S-expression and then serialising it again gets the same result. *)
 let test_sexp () =
   let test name s =
-    let s = remove_indent s in
+    let s = String.trim (remove_indent s) in
     let s1 = Sexplib.Sexp.of_string s in
     let spec = Spec.t_of_sexp s1 in
     let s2 = Spec.sexp_of_t spec in
@@ -463,7 +462,7 @@ let test_sexp () =
 let test_docker () =
   let test ~buildkit name expect sexp =
     let spec = Spec.t_of_sexp (Sexplib.Sexp.of_string sexp) in
-    let got = Obuilder_spec.Docker.dockerfile_of_spec ~buildkit spec |> Dockerfile.string_of_t in
+    let got = Obuilder_spec.Docker.dockerfile_of_spec ~buildkit spec in
     let expect = remove_indent expect in
     Alcotest.(check string) name expect got
   in
@@ -528,6 +527,7 @@ let test_docker () =
   test ~buildkit:false "Multi-stage"
     {| FROM base as tools
        RUN make tools
+
        FROM base
        COPY --from=tools binary /usr/local/bin/
     |} {|