diff --git a/.github/workflows/gh-pages.yml b/.github/workflows/gh-pages.yml
index 82423cac..58a8bfe1 100644
--- a/.github/workflows/gh-pages.yml
+++ b/.github/workflows/gh-pages.yml
@@ -15,7 +15,7 @@ jobs:
       - name: Use OCaml
         uses: ocaml/setup-ocaml@v3
         with:
-          ocaml-compiler: '5.0'
+          ocaml-compiler: '5.3'
           dune-cache: true
           allow-prerelease-opam: true
 
diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 894b13ba..6b97c607 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -16,8 +16,8 @@ jobs:
         os:
             - ubuntu-latest
         ocaml-compiler:
-            - '4.14'
-            - '5.2'
+            - '5.0'
+            - '5.3'
 
     runs-on: ${{ matrix.os }}
     steps:
@@ -32,15 +32,10 @@ jobs:
       - run: opam pin picos 0.6.0 -y -n
 
       - run: opam install -t moonpool moonpool-lwt moonpool-io --deps-only
-        if: matrix.ocaml-compiler == '5.2'
-      - run: opam install -t moonpool --deps-only
-        if: matrix.ocaml-compiler != '5.2'
       - run: opam exec -- dune build @install
 
       # install some depopts
       - run: opam install thread-local-storage trace hmap
-        if: matrix.ocaml-compiler == '5.2'
-
       - run: opam exec -- dune build --profile=release --force @install @runtest
 
   compat:
diff --git a/dune-project b/dune-project
index 7f1de178..ceae9ab2 100644
--- a/dune-project
+++ b/dune-project
@@ -16,7 +16,7 @@
  (name moonpool)
  (synopsis "Pools of threads supported by a pool of domains")
  (depends
-  (ocaml (>= 4.14))
+  (ocaml (>= 5.0))
   dune
   (either (>= 1.0))
   (trace :with-test)
diff --git a/src/core/chan.ml b/src/core/chan.ml
index be4ac3b9..57c4b4b5 100644
--- a/src/core/chan.ml
+++ b/src/core/chan.ml
@@ -70,8 +70,6 @@ let close (self : _ t) : unit =
   Mutex.unlock self.mutex;
   Queue.iter Trigger.signal q
 
-[@@@ifge 5.0]
-
 let rec push (self : _ t) x : unit =
   Mutex.lock self.mutex;
 
@@ -120,5 +118,3 @@ let rec pop (self : 'a t) : 'a =
     Mutex.unlock self.mutex;
     Trigger.await_exn tr;
     pop self
-
-[@@@endif]
diff --git a/src/core/chan.mli b/src/core/chan.mli
index a4898069..8d0a10b5 100644
--- a/src/core/chan.mli
+++ b/src/core/chan.mli
@@ -28,8 +28,6 @@ val close : _ t -> unit
 (** Close the channel. Further push and pop calls will fail. This is idempotent.
 *)
 
-[@@@ifge 5.0]
-
 val push : 'a t -> 'a -> unit
 (** Push the value into the channel, suspending the current task if the channel
     is currently full.
@@ -48,5 +46,3 @@ val pop_block_exn : 'a t -> 'a
     The precautions around blocking from inside a thread pool
     are the same as explained in {!Fut.wait_block}. *)
 *)
-
-[@@@endif]
diff --git a/src/core/dune b/src/core/dune
index 015e9ce6..1be87695 100644
--- a/src/core/dune
+++ b/src/core/dune
@@ -12,7 +12,4 @@
   moonpool.dpool
   (re_export picos))
  (flags :standard -open Moonpool_private)
- (private_modules util_pool_)
- (preprocess
-  (action
-   (run %{project_root}/src/cpp/cpp.exe %{input-file}))))
+ (private_modules util_pool_))
diff --git a/src/core/fut.ml b/src/core/fut.ml
index 415e68ab..715ba560 100644
--- a/src/core/fut.ml
+++ b/src/core/fut.ml
@@ -1,4 +1,4 @@
-module A = Atomic_
+module A = Atomic
 module C = Picos.Computation
 
 type 'a or_error = ('a, Exn_bt.t) result
@@ -424,8 +424,6 @@ let wait_block self =
     let bt = Printexc.get_raw_backtrace () in
     Error (Exn_bt.make exn bt)
 
-[@@@ifge 5.0]
-
 let await (self : 'a t) : 'a =
   (* fast path: peek *)
   match C.peek_exn self with
@@ -439,8 +437,6 @@ let await (self : 'a t) : 'a =
     (* un-suspended: we should have a result! *)
     get_or_fail_exn self
 
-[@@@endif]
-
 module Infix = struct
   let[@inline] ( >|= ) x f = map ~f x
   let[@inline] ( >>= ) x f = bind ~f x
diff --git a/src/core/fut.mli b/src/core/fut.mli
index 45c800df..073e393f 100644
--- a/src/core/fut.mli
+++ b/src/core/fut.mli
@@ -236,8 +236,6 @@ val for_list : on:Runner.t -> 'a list -> ('a -> unit) -> unit t
 
     {b NOTE} This is only available on OCaml 5. *)
 
-[@@@ifge 5.0]
-
 val await : 'a t -> 'a
 (** [await fut] suspends the current tasks until [fut] is fulfilled, then
     resumes the task on this same runner (but possibly on a different
@@ -248,8 +246,6 @@ val await : 'a t -> 'a
     This must only be run from inside the runner itself. The runner must support
     {!Suspend_}. {b NOTE}: only on OCaml 5.x *)
 
-[@@@endif]
-
 (** {2 Blocking} *)
 
 val wait_block : 'a t -> 'a or_error
diff --git a/src/core/moonpool.ml b/src/core/moonpool.ml
index d9f72b51..6b9aebe0 100644
--- a/src/core/moonpool.ml
+++ b/src/core/moonpool.ml
@@ -12,15 +12,10 @@ let get_current_runner = Runner.get_current_runner
 let recommended_thread_count () = Domain_.recommended_number ()
 let spawn = Fut.spawn
 let spawn_on_current_runner = Fut.spawn_on_current_runner
-
-[@@@ifge 5.0]
-
 let await = Fut.await
 let yield = Picos.Fiber.yield
 
-[@@@endif]
-
-module Atomic = Atomic_
+module Atomic = Atomic
 module Blocking_queue = Bb_queue
 module Background_thread = Background_thread
 module Chan = Chan
diff --git a/src/core/moonpool.mli b/src/core/moonpool.mli
index 3a5f5eef..0e80fa2f 100644
--- a/src/core/moonpool.mli
+++ b/src/core/moonpool.mli
@@ -72,8 +72,6 @@ val get_current_runner : unit -> Runner.t option
 (** See {!Runner.get_current_runner}
     @since 0.7 *)
 
-[@@@ifge 5.0]
-
 val await : 'a Fut.t -> 'a
 (** Await a future, must be run on a moonpool runner. See {!Fut.await}. Only on
     OCaml >= 5.0.
@@ -84,8 +82,6 @@ val yield : unit -> unit
     >= 5.0.
     @since NEXT_RELEASE *)
 
-[@@@endif]
-
 module Lock = Lock
 module Fut = Fut
 module Chan = Chan
@@ -203,7 +199,7 @@ module Blocking_queue : sig
       @since 0.4 *)
 end
 
-module Atomic = Atomic_
+module Atomic = Atomic
 (** Atomic values.
 
     This is either a shim using [ref], on pre-OCaml 5, or the standard [Atomic]
diff --git a/src/core/worker_loop_.ml b/src/core/worker_loop_.ml
index 51cd75cd..bd2cd5ca 100644
--- a/src/core/worker_loop_.ml
+++ b/src/core/worker_loop_.ml
@@ -33,8 +33,6 @@ type 'st ops = {
 (** A dummy task. *)
 let _dummy_task : task_full = T_start { f = ignore; fiber = _dummy_fiber }
 
-[@@@ifge 5.0]
-
 let[@inline] discontinue k exn =
   let bt = Printexc.get_raw_backtrace () in
   Effect.Deep.discontinue_with_backtrace k exn bt
@@ -100,12 +98,6 @@ let with_handler (type st arg) ~(ops : st ops) (self : st) :
   let handler = Effect.Deep.{ retc = Fun.id; exnc = raise_with_bt; effc } in
   fun f -> Effect.Deep.match_with f () handler
 
-[@@@else_]
-
-let with_handler ~ops:_ self f = f ()
-
-[@@@endif]
-
 let worker_loop (type st) ~block_signals ~(ops : st ops) (self : st) : unit =
   if block_signals then (
     try
diff --git a/src/core/ws_pool.ml b/src/core/ws_pool.ml
index 137e76cd..1b95cd16 100644
--- a/src/core/ws_pool.ml
+++ b/src/core/ws_pool.ml
@@ -1,5 +1,5 @@
 open Types_
-module A = Atomic_
+module A = Atomic
 module WSQ = Ws_deque_
 module WL = Worker_loop_
 include Runner
diff --git a/src/cpp/cpp.ml b/src/cpp/cpp.ml
deleted file mode 100644
index b4df7a1a..00000000
--- a/src/cpp/cpp.ml
+++ /dev/null
@@ -1,124 +0,0 @@
-type op =
-  | Le
-  | Ge
-
-type line =
-  | If of op * int * int
-  | Elseif of op * int * int
-  | Else
-  | Endif
-  | Raw of string
-  | Eof
-
-let prefix ~pre s =
-  let len = String.length pre in
-  if len > String.length s then
-    false
-  else (
-    let rec check i =
-      if i = len then
-        true
-      else if String.unsafe_get s i <> String.unsafe_get pre i then
-        false
-      else
-        check (i + 1)
-    in
-    check 0
-  )
-
-let eval ~major ~minor op i j =
-  match op with
-  | Le -> (major, minor) <= (i, j)
-  | Ge -> (major, minor) >= (i, j)
-
-let preproc_lines ~file ~major ~minor (ic : in_channel) : unit =
-  let pos = ref 0 in
-  let fail msg =
-    failwith (Printf.sprintf "at line %d in '%s': %s" !pos file msg)
-  in
-  let pp_pos () = Printf.printf "#%d %S\n" !pos file in
-
-  let parse_line () : line =
-    match input_line ic with
-    | exception End_of_file -> Eof
-    | line ->
-      let line' = String.trim line in
-      incr pos;
-      if line' <> "" && line'.[0] = '[' then
-        if prefix line' ~pre:"[@@@ifle" then
-          Scanf.sscanf line' "[@@@ifle %d.%d]" (fun x y -> If (Le, x, y))
-        else if prefix line' ~pre:"[@@@ifge" then
-          Scanf.sscanf line' "[@@@ifge %d.%d]" (fun x y -> If (Ge, x, y))
-        else if prefix line' ~pre:"[@@@elifle" then
-          Scanf.sscanf line' "[@@@elifle %d.%d]" (fun x y -> Elseif (Le, x, y))
-        else if prefix line' ~pre:"[@@@elifge" then
-          Scanf.sscanf line' "[@@@elifge %d.%d]" (fun x y -> Elseif (Ge, x, y))
-        else if line' = "[@@@else_]" then
-          Else
-        else if line' = "[@@@endif]" then
-          Endif
-        else
-          Raw line
-      else
-        Raw line
-  in
-
-  (* entry point *)
-  let rec top () =
-    match parse_line () with
-    | Eof -> ()
-    | If (op, i, j) ->
-      if eval ~major ~minor op i j then (
-        pp_pos ();
-        cat_block ()
-      ) else
-        skip_block ~elseok:true ()
-    | Raw s ->
-      print_endline s;
-      top ()
-    | Elseif _ | Else | Endif -> fail "unexpected elseif|else|endif"
-  (* current block is the valid one *)
-  and cat_block () =
-    match parse_line () with
-    | Eof -> fail "unexpected EOF"
-    | If _ -> fail "nested if not supported"
-    | Raw s ->
-      print_endline s;
-      cat_block ()
-    | Endif ->
-      pp_pos ();
-      top ()
-    | Elseif _ | Else -> skip_block ~elseok:false ()
-  (* skip current block.
-     @param elseok if true, we should evaluate "elseif" *)
-  and skip_block ~elseok () =
-    match parse_line () with
-    | Eof -> fail "unexpected EOF"
-    | If _ -> fail "nested if not supported"
-    | Raw _ -> skip_block ~elseok ()
-    | Endif ->
-      pp_pos ();
-      top ()
-    | Elseif (op, i, j) ->
-      if elseok && eval ~major ~minor op i j then (
-        pp_pos ();
-        cat_block ()
-      ) else
-        skip_block ~elseok ()
-    | Else ->
-      if elseok then (
-        pp_pos ();
-        cat_block ()
-      ) else
-        skip_block ~elseok ()
-  in
-  top ()
-
-let () =
-  let file = Sys.argv.(1) in
-  let version = Sys.ocaml_version in
-  let major, minor = Scanf.sscanf version "%u.%u" (fun maj min -> maj, min) in
-  let ic = open_in file in
-  preproc_lines ~file ~major ~minor ic;
-
-  ()
diff --git a/src/cpp/dune b/src/cpp/dune
deleted file mode 100644
index c4c75e8b..00000000
--- a/src/cpp/dune
+++ /dev/null
@@ -1,6 +0,0 @@
-; our little preprocessor (ported from containers)
-
-(executable
- (name cpp)
- (modes
-  (best exe)))
diff --git a/src/dpool/dune b/src/dpool/dune
index 23c91d38..810a6097 100644
--- a/src/dpool/dune
+++ b/src/dpool/dune
@@ -2,8 +2,5 @@
  (name moonpool_dpool)
  (public_name moonpool.dpool)
  (synopsis "Moonpool's domain pool (used to start worker threads)")
- (preprocess
-  (action
-   (run %{project_root}/src/cpp/cpp.exe %{input-file})))
  (flags :standard -open Moonpool_private)
  (libraries moonpool.private))
diff --git a/src/dpool/moonpool_dpool.ml b/src/dpool/moonpool_dpool.ml
index 5f177362..42917c1a 100644
--- a/src/dpool/moonpool_dpool.ml
+++ b/src/dpool/moonpool_dpool.ml
@@ -71,7 +71,7 @@ type event =
     new threads for pools. *)
 type worker_state = {
   q: event Bb_queue.t;
-  th_count: int Atomic_.t;  (** Number of threads on this *)
+  th_count: int Atomic.t;  (** Number of threads on this *)
 }
 
 (** Array of (optional) workers.
@@ -101,14 +101,14 @@ let work_ idx (st : worker_state) : unit =
       match Bb_queue.pop st.q with
       | Run f -> (try f () with _ -> ())
       | Decr ->
-        if Atomic_.fetch_and_add st.th_count (-1) = 1 then (
+        if Atomic.fetch_and_add st.th_count (-1) = 1 then (
           continue := false;
 
           (* wait a bit, we might be needed again in a short amount of time *)
           try
             for _n_attempt = 1 to 50 do
               Thread.delay 0.001;
-              if Atomic_.get st.th_count > 0 then (
+              if Atomic.get st.th_count > 0 then (
                 (* needed again! *)
                 continue := true;
                 raise Exit
@@ -129,7 +129,7 @@ let work_ idx (st : worker_state) : unit =
         | Some _st', dom ->
           assert (st == _st');
 
-          if Atomic_.get st.th_count > 0 then
+          if Atomic.get st.th_count > 0 then
             (* still alive! *)
             (Some st, dom), true
           else
@@ -145,7 +145,7 @@ let work_ idx (st : worker_state) : unit =
 (* special case for main domain: we start a worker immediately *)
 let () =
   assert (Domain_.is_main_domain ());
-  let w = { th_count = Atomic_.make 1; q = Bb_queue.create () } in
+  let w = { th_count = Atomic.make 1; q = Bb_queue.create () } in
   (* thread that stays alive *)
   ignore (Thread.create (fun () -> work_ 0 w) () : Thread.t);
   domains_.(0) <- Lock.create (Some w, None)
@@ -157,12 +157,12 @@ let run_on (i : int) (f : unit -> unit) : unit =
   let w =
     Lock.update_map domains_.(i) (function
       | (Some w, _) as st ->
-        Atomic_.incr w.th_count;
+        Atomic.incr w.th_count;
         st, w
       | None, dying_dom ->
         (* join previous dying domain, to free its resources, if any *)
         Option.iter Domain_.join dying_dom;
-        let w = { th_count = Atomic_.make 1; q = Bb_queue.create () } in
+        let w = { th_count = Atomic.make 1; q = Bb_queue.create () } in
         let worker : domain = Domain_.spawn (fun () -> work_ i w) in
         (Some w, Some worker), w)
   in
diff --git a/src/private/domain_.ml b/src/private/domain_.ml
index 3050282f..f3605f39 100644
--- a/src/private/domain_.ml
+++ b/src/private/domain_.ml
@@ -1,4 +1,3 @@
-[@@@ifge 5.0]
 [@@@ocaml.alert "-unstable"]
 
 let recommended_number () = Domain.recommended_domain_count ()
@@ -10,18 +9,3 @@ let spawn : _ -> t = Domain.spawn
 let relax = Domain.cpu_relax
 let join = Domain.join
 let is_main_domain = Domain.is_main_domain
-
-[@@@ocaml.alert "+unstable"]
-[@@@else_]
-
-let recommended_number () = 1
-
-type t = Thread.t
-
-let get_id (self : t) : int = Thread.id self
-let spawn f : t = Thread.create f ()
-let relax () = Thread.yield ()
-let join = Thread.join
-let is_main_domain () = true
-
-[@@@endif]
diff --git a/src/private/dune b/src/private/dune
index 4555122c..75c918b8 100644
--- a/src/private/dune
+++ b/src/private/dune
@@ -2,9 +2,6 @@
  (name moonpool_private)
  (public_name moonpool.private)
  (synopsis "Private internal utils for Moonpool (do not rely on)")
- (preprocess
-  (action
-   (run %{project_root}/src/cpp/cpp.exe %{input-file})))
  (libraries
   threads
   either
diff --git a/src/private/ws_deque_.ml b/src/private/ws_deque_.ml
index 368cc8b0..d54a3992 100644
--- a/src/private/ws_deque_.ml
+++ b/src/private/ws_deque_.ml
@@ -1,4 +1,4 @@
-module A = Atomic_
+module A = Atomic
 
 (* terminology: