diff --git a/src/core/lwt_pool.ml b/src/core/lwt_pool.ml
index 1605bc89f..bf06787ab 100644
--- a/src/core/lwt_pool.ml
+++ b/src/core/lwt_pool.ml
@@ -108,7 +108,7 @@ let validate_and_return p c =
             resolver is waiting. *)
          dispose p c >>= fun () ->
          replace_disposed p;
-         Lwt.fail e)
+         Lwt.reraise e)
 
 (* Acquire a pool member. *)
 let acquire p =
diff --git a/src/core/lwt_seq.ml b/src/core/lwt_seq.ml
index fe40eadfb..dd3f0396f 100644
--- a/src/core/lwt_seq.ml
+++ b/src/core/lwt_seq.ml
@@ -270,7 +270,7 @@ let rec unfold f u () =
   match f u with
   | None -> return_nil
   | Some (x, u') -> Lwt.return (Cons (x, unfold f u'))
-  | exception exc when Lwt.Exception_filter.run exc -> Lwt.fail exc
+  | exception exc when Lwt.Exception_filter.run exc -> Lwt.reraise exc
 
 let rec unfold_lwt f u () =
   let* x = f u in
@@ -299,7 +299,7 @@ let rec of_seq seq () =
   | Seq.Nil -> return_nil
   | Seq.Cons (x, next) ->
     Lwt.return (Cons (x, (of_seq next)))
-  | exception exn when Lwt.Exception_filter.run exn -> Lwt.fail exn
+  | exception exn when Lwt.Exception_filter.run exn -> Lwt.reraise exn
 
 let rec of_seq_lwt (seq: 'a Lwt.t Seq.t): 'a t = fun () ->
     match seq () with
@@ -315,4 +315,4 @@ let of_seq_lwt (seq: 'a Lwt.t Seq.t): 'a t = fun () ->
        let+ x = x in
        let next = of_seq_lwt next in
        Cons (x, next)
-    | exception exc when Lwt.Exception_filter.run exc -> Lwt.fail exc
+    | exception exc when Lwt.Exception_filter.run exc -> Lwt.reraise exc
diff --git a/src/core/lwt_stream.ml b/src/core/lwt_stream.ml
index 88e83f449..cb7539405 100644
--- a/src/core/lwt_stream.ml
+++ b/src/core/lwt_stream.ml
@@ -279,9 +279,9 @@ class ['a] bounded_push_impl (info : 'a push_bounded) wakener_cell last close =
              let waiter, wakener = Lwt.task () in
              info.pushb_push_waiter <- waiter;
              info.pushb_push_wakener <- wakener;
-             Lwt.fail exn
+             Lwt.reraise exn
            | _ ->
-             Lwt.fail exn)
+             Lwt.reraise exn)
     end else begin
       (* Push the element at the end of the queue. *)
       enqueue' (Some x) last;
@@ -367,11 +367,18 @@ let feed s =
     else begin
       (* Otherwise request a new element. *)
       let thread =
-        from.from_create () >>= fun x ->
-        (* Push the element to the end of the queue. *)
-        enqueue x s;
-        if x = None then Lwt.wakeup s.close ();
-        Lwt.return_unit
+        (* The function [from_create] can raise an exception (with
+           [raise], rather than returning a failed promise with
+           [Lwt.fail]). In this case, we have to catch the exception
+           and turn it into a safe failed promise. *)
+        Lwt.catch
+          (fun () ->
+            from.from_create () >>= fun x ->
+            (* Push the element to the end of the queue. *)
+            enqueue x s;
+            if x = None then Lwt.wakeup s.close ();
+            Lwt.return_unit)
+          Lwt.reraise
       in
       (* Allow other threads to access this thread. *)
       from.from_thread <- thread;
@@ -1070,7 +1077,7 @@ let parse s f =
     (fun () -> f s)
     (fun exn ->
        s.node <- node;
-       Lwt.fail exn)
+       Lwt.reraise exn)
 
 let hexdump stream =
   let buf = Buffer.create 80 and num = ref 0 in
diff --git a/src/ppx/ppx_lwt.ml b/src/ppx/ppx_lwt.ml
index c2030be23..e77486c1a 100644
--- a/src/ppx/ppx_lwt.ml
+++ b/src/ppx/ppx_lwt.ml
@@ -23,7 +23,7 @@ let add_wildcard_case cases =
   if not has_wildcard
   then cases
        @ (let loc = Location.none in
-          [case ~lhs:[%pat? exn] ~guard:None ~rhs:[%expr Lwt.fail exn]])
+          [case ~lhs:[%pat? exn] ~guard:None ~rhs:[%expr Lwt.reraise exn]])
   else cases
 
 (** {3 Internal names} *)
@@ -154,11 +154,11 @@ let lwt_expression mapper exp attributes ext_loc =
     Some (mapper#expression { new_exp with pexp_attributes })
 
   (* [assert%lwt $e$] ≡
-     [try Lwt.return (assert $e$) with exn -> Lwt.fail exn] *)
+     [try Lwt.return (assert $e$) with exn -> Lwt.reraise exn] *)
   | Pexp_assert e ->
     let new_exp =
       let loc = !default_loc in
-      [%expr try Lwt.return (assert [%e e]) with exn -> Lwt.fail exn]
+      [%expr try Lwt.return (assert [%e e]) with exn -> Lwt.reraise exn]
     in
     Some (mapper#expression { new_exp with pexp_attributes })
 
diff --git a/src/ppx/ppx_lwt.mli b/src/ppx/ppx_lwt.mli
index 1d3a541e6..0912c07e0 100644
--- a/src/ppx/ppx_lwt.mli
+++ b/src/ppx/ppx_lwt.mli
@@ -80,10 +80,10 @@ catch (fun () -> f x)
         prerr_endline msg;
         return ()
     | exn ->
-        Lwt.fail exn)
+        Lwt.reraise exn)
    ]}
 
-   Note that the [exn -> Lwt.fail exn] branch is automatically added
+   Note that the [exn -> Lwt.reraise exn] branch is automatically added
    when needed.
 
    - finalizer:
diff --git a/src/unix/lwt_io.ml b/src/unix/lwt_io.ml
index cf0b18bf0..8b3033fae 100644
--- a/src/unix/lwt_io.ml
+++ b/src/unix/lwt_io.ml
@@ -231,7 +231,7 @@ let perform_io : type mode. mode _channel -> int Lwt.t = fun ch ->
             (function
               | Unix.Unix_error (Unix.EPIPE, _, _) ->
                 Lwt.return 0
-              | exn -> Lwt.fail exn) [@ocaml.warning "-4"]
+              | exn -> Lwt.reraise exn) [@ocaml.warning "-4"]
         else
           perform ch.buffer ptr len
       in
@@ -525,7 +525,7 @@ let make :
     max = (match mode with
       | Input -> 0
       | Output -> size);
-    close = lazy(Lwt.catch close Lwt.fail);
+    close = lazy(Lwt.catch close Lwt.reraise);
     abort_waiter = abort_waiter;
     abort_wakener = abort_wakener;
     main = wrapper;
@@ -537,7 +537,7 @@ let make :
         perform_io,
         fun pos cmd ->
           try seek pos cmd
-          with e when Lwt.Exception_filter.run e -> Lwt.fail e
+          with e when Lwt.Exception_filter.run e -> Lwt.reraise e
     );
   } and wrapper = {
     state = Idle;
@@ -678,7 +678,7 @@ struct
     let ptr = ic.ptr in
     if ptr = ic.max then
       refill ic >>= function
-      | 0 -> Lwt.fail End_of_file
+      | 0 -> raise End_of_file
       | _ -> read_char ic
     else begin
       ic.ptr <- ptr + 1;
@@ -690,7 +690,7 @@ struct
       (fun () -> read_char ic >|= fun ch -> Some ch)
       (function
         | End_of_file -> Lwt.return_none
-        | exn -> Lwt.fail exn)
+        | exn -> Lwt.reraise exn)
 
   let read_line ic =
     let buf = Buffer.create 128 in
@@ -711,7 +711,7 @@ struct
             if cr_read then Buffer.add_char buf '\r';
             Lwt.return(Buffer.contents buf)
           | exn ->
-            Lwt.fail exn)
+            Lwt.reraise exn)
     in
     read_char ic >>= function
     | '\r' -> loop true
@@ -723,7 +723,7 @@ struct
       (fun () -> read_line ic >|= fun ch -> Some ch)
       (function
         | End_of_file -> Lwt.return_none
-        | exn -> Lwt.fail exn)
+        | exn -> Lwt.reraise exn)
 
   let unsafe_read_into' ic blit buf ofs len =
     let avail = ic.max - ic.ptr in
@@ -771,7 +771,7 @@ struct
     let rec loop ic buf ofs len =
       read_into ic buf ofs len >>= function
       | 0 ->
-          Lwt.fail End_of_file
+          raise End_of_file
       | n ->
           let len = len - n in
           if len = 0 then
@@ -985,7 +985,7 @@ struct
     if ic.max - ic.ptr < size then
       refill ic >>= function
       | 0 ->
-        Lwt.fail End_of_file
+        raise End_of_file
       | _ ->
         read_block_unsafe ic size f
     else begin
@@ -1440,7 +1440,7 @@ let open_temp_file ?buffer ?flags ?perm ?temp_dir ?prefix ?(suffix = "") () =
         Lwt.return (fname, chan))
       (function
         | Unix.Unix_error _ when n < 1000 -> attempt (n + 1)
-        | exn -> Lwt.fail exn)
+        | exn -> Lwt.reraise exn)
   in
   attempt 0
 
@@ -1468,7 +1468,7 @@ let create_temp_dir
         Lwt.return name)
       (function
       | Unix.Unix_error (Unix.EEXIST, _, _) when n < 1000 -> attempt (n + 1)
-      | exn -> Lwt.fail exn)
+      | exn -> Lwt.reraise exn)
   in
   attempt 0
 
@@ -1489,10 +1489,10 @@ let win32_unlink fn =
                 (* If everything succeeded but the final removal still failed,
                    restore original permissions *)
                 Lwt_unix.chmod fn st_perm >>= fun () ->
-                Lwt.fail exn)
+                Lwt.reraise exn)
          )
-         (fun _ -> Lwt.fail exn)
-     | exn -> Lwt.fail exn)
+         (fun _ -> Lwt.reraise exn)
+     | exn -> Lwt.reraise exn)
 
 let unlink =
   if Sys.win32 then
@@ -1549,7 +1549,7 @@ let close_socket fd =
          (function
            (* Occurs if the peer closes the connection first. *)
            | Unix.Unix_error (Unix.ENOTCONN, _, _) -> Lwt.return_unit
-           | exn -> Lwt.fail exn) [@ocaml.warning "-4"])
+           | exn -> Lwt.reraise exn) [@ocaml.warning "-4"])
     (fun () ->
        Lwt_unix.close fd)
 
@@ -1574,7 +1574,7 @@ let open_connection ?fd ?in_buffer ?out_buffer sockaddr =
                      ~mode:output (Lwt_bytes.write fd)))
     (fun exn ->
        Lwt_unix.close fd >>= fun () ->
-       Lwt.fail exn)
+       Lwt.reraise exn)
 
 let with_close_connection f (ic, oc) =
   (* If the user already tried to close the socket and got an exception, we
@@ -1639,7 +1639,7 @@ let establish_server_generic
         (function
           | Unix.Unix_error (Unix.ECONNABORTED, _, _) ->
             Lwt.return `Try_again
-          | e -> Lwt.fail e)
+          | e -> Lwt.reraise e)
     in
 
     Lwt.pick [try_to_accept; should_stop] >>= function
diff --git a/src/unix/lwt_process.cppo.ml b/src/unix/lwt_process.cppo.ml
index 791e38ba7..ceb86be23 100644
--- a/src/unix/lwt_process.cppo.ml
+++ b/src/unix/lwt_process.cppo.ml
@@ -378,7 +378,7 @@ let read_opt read ic =
     (function
       | Unix.Unix_error (Unix.EPIPE, _, _) | End_of_file ->
         Lwt.return_none
-      | exn -> Lwt.fail exn) [@ocaml.warning "-4"]
+      | exn -> Lwt.reraise exn) [@ocaml.warning "-4"]
 
 let recv_chars pr =
   let ic = pr#stdout in
@@ -512,8 +512,8 @@ let pmap ?timeout ?env ?cwd ?stderr cmd text =
       | Lwt.Canceled as exn ->
         (* Cancel the getter if the sender was canceled. *)
         Lwt.cancel getter;
-        Lwt.fail exn
-      | exn -> Lwt.fail exn)
+        Lwt.reraise exn
+      | exn -> Lwt.reraise exn)
 
 let pmap_chars ?timeout ?env ?cwd ?stderr cmd chars =
   let pr = open_process ?timeout ?env ?cwd ?stderr cmd in
@@ -534,8 +534,8 @@ let pmap_line ?timeout ?env ?cwd ?stderr cmd line =
       | Lwt.Canceled as exn ->
         (* Cancel the getter if the sender was canceled. *)
         Lwt.cancel getter;
-        Lwt.fail exn
-      | exn -> Lwt.fail exn)
+        Lwt.reraise exn
+      | exn -> Lwt.reraise exn)
 
 let pmap_lines ?timeout ?env ?cwd ?stderr cmd lines =
   let pr = open_process ?timeout ?env ?cwd ?stderr cmd in
diff --git a/src/unix/lwt_unix.cppo.ml b/src/unix/lwt_unix.cppo.ml
index 20f73378e..5edb4b83d 100644
--- a/src/unix/lwt_unix.cppo.ml
+++ b/src/unix/lwt_unix.cppo.ml
@@ -147,7 +147,7 @@ let auto_pause timeout =
 
 exception Timeout
 
-let timeout d = sleep d >>= fun () -> Lwt.fail Timeout
+let timeout d = sleep d >>= fun () -> raise Timeout
 
 let with_timeout d f = Lwt.pick [timeout d; Lwt.apply f ()]
 
@@ -582,7 +582,7 @@ let wrap_syscall event ch action =
   | Retry_write ->
     register_action Write ch action
   | e when Lwt.Exception_filter.run e ->
-    Lwt.fail e
+    Lwt.reraise e
 
 (* +-----------------------------------------------------------------+
    | Basic file input/output                                         |
@@ -636,7 +636,7 @@ let wait_read ch =
          Lwt.return_unit
        else
          register_action Read ch ignore)
-    Lwt.fail
+    Lwt.reraise
 
 external stub_read : Unix.file_descr -> Bytes.t -> int -> int -> int = "lwt_unix_read"
 external read_job : Unix.file_descr -> Bytes.t -> int -> int -> int job = "lwt_unix_read_job"
@@ -694,7 +694,7 @@ let wait_write ch =
          Lwt.return_unit
        else
          register_action Write ch ignore)
-    Lwt.fail
+    Lwt.reraise
 
 external stub_write : Unix.file_descr -> Bytes.t -> int -> int -> int = "lwt_unix_write"
 external write_job : Unix.file_descr -> Bytes.t -> int -> int -> int job = "lwt_unix_write_job"
@@ -1034,7 +1034,7 @@ let file_exists name =
     (fun e ->
        match e with
        | Unix.Unix_error _ -> Lwt.return_false
-       | _ -> Lwt.fail e) [@ocaml.warning "-4"]
+       | _ -> Lwt.reraise e) [@ocaml.warning "-4"]
 
 external utimes_job : string -> float -> float -> unit job =
   "lwt_unix_utimes_job"
@@ -1140,7 +1140,7 @@ struct
       (fun e ->
          match e with
          | Unix.Unix_error _ -> Lwt.return_false
-         | _ -> Lwt.fail e) [@ocaml.warning "-4"]
+         | _ -> Lwt.reraise e) [@ocaml.warning "-4"]
 
 end
 
@@ -1408,7 +1408,7 @@ let files_of_directory path =
               (fun () -> readdir_n handle chunk_size)
               (fun exn ->
                  closedir handle >>= fun () ->
-                 Lwt.fail exn) >>= fun entries ->
+                 Lwt.reraise exn) >>= fun entries ->
             if Array.length entries < chunk_size then begin
               state := LDS_done;
               closedir handle >>= fun () ->
@@ -1423,7 +1423,7 @@ let files_of_directory path =
               (fun () -> readdir_n handle chunk_size)
               (fun exn ->
                  closedir handle >>= fun () ->
-                 Lwt.fail exn) >>= fun entries ->
+                 Lwt.reraise exn) >>= fun entries ->
             if Array.length entries < chunk_size then begin
               state := LDS_done;
               closedir handle >>= fun () ->
@@ -2395,7 +2395,7 @@ let () =
 let _waitpid flags pid =
   Lwt.catch
     (fun () -> Lwt.return (Unix.waitpid flags pid))
-    Lwt.fail
+    Lwt.reraise
 
 let waitpid =
   if Sys.win32 then
diff --git a/test/core/test_lwt.ml b/test/core/test_lwt.ml
index 3a08fdc32..2ba5ab564 100644
--- a/test/core/test_lwt.ml
+++ b/test/core/test_lwt.ml
@@ -549,6 +549,15 @@ let catch_tests = suite "catch" [
     state_is (Lwt.Return Exception) p
   end;
 
+  test "rejected (raise)" begin fun () ->
+    let p =
+      Lwt.catch
+        (fun () -> raise Exception)
+        (fun exn -> Lwt.return exn)
+    in
+    state_is (Lwt.Return Exception) p
+  end;
+
   (* This is an analog of the "bind quirk," see
 
        https://github.com/ocsigen/lwt/issues/329 *)
@@ -696,7 +705,7 @@ let backtrace_catch_tests = suite "backtrace_catch" [
   test "rejected" begin fun () ->
     let p =
       Lwt.backtrace_catch add_loc
-        (fun () -> Lwt.fail Exception)
+        (fun () -> raise Exception)
         (fun exn -> Lwt.return exn)
     in
     state_is (Lwt.Return Exception) p
@@ -789,7 +798,7 @@ let try_bind_tests = suite "try_bind" [
   test "rejected" begin fun () ->
     let p =
       Lwt.try_bind
-        (fun () -> Lwt.fail Exception)
+        (fun () -> raise Exception)
         (fun _ -> Lwt.return Exit)
         (fun exn -> Lwt.return exn)
     in
@@ -810,7 +819,7 @@ let try_bind_tests = suite "try_bind" [
   test "rejected, h raises" begin fun () ->
     try
       ignore @@ Lwt.try_bind
-        (fun () -> Lwt.fail Exit)
+        (fun () -> raise Exit)
         (fun _ -> Lwt.return_unit)
         (fun _ -> raise Exception);
       Lwt.return_false
@@ -961,7 +970,7 @@ let backtrace_try_bind_tests = suite "backtrace_try_bind" [
   test "rejected" begin fun () ->
     let p =
       Lwt.backtrace_try_bind add_loc
-        (fun () -> Lwt.fail Exception)
+        (fun () -> raise Exception)
         (fun _ -> Lwt.return Exit)
         (fun exn -> Lwt.return exn)
     in
@@ -1132,7 +1141,7 @@ let finalize_tests = suite "finalize" [
   test "rejected, f' raises" begin fun () ->
     try
       ignore @@ Lwt.finalize
-        (fun () -> Lwt.fail Exit)
+        (fun () -> raise Exit)
         (fun () -> raise Exception);
       Lwt.return_false
     with Exception ->
@@ -1169,7 +1178,7 @@ let finalize_tests = suite "finalize" [
     let p =
       Lwt.finalize
         (fun () -> p)
-        (fun () -> Lwt.fail Exception)
+        (fun () -> raise Exception)
     in
     Lwt.wakeup r ();
     state_is (Lwt.Fail Exception) p
@@ -1232,7 +1241,7 @@ let finalize_tests = suite "finalize" [
     let p =
       Lwt.finalize
         (fun () -> p)
-        (fun () -> Lwt.fail Exception)
+        (fun () -> raise Exception)
     in
     Lwt.wakeup_exn r Exit;
     state_is (Lwt.Fail Exception) p
@@ -1347,7 +1356,7 @@ let backtrace_finalize_tests = suite "backtrace_finalize" [
     let f'_ran = ref false in
     let p =
       Lwt.backtrace_finalize add_loc
-        (fun () -> Lwt.fail Exception)
+        (fun () -> raise Exception)
         (fun () -> f'_ran := true; Lwt.return_unit)
     in
     Lwt.bind (state_is (Lwt.Fail Exception) p) (fun correct ->
@@ -1367,7 +1376,7 @@ let backtrace_finalize_tests = suite "backtrace_finalize" [
   test "rejected, f' raises" begin fun () ->
     try
       ignore @@ Lwt.backtrace_finalize add_loc
-        (fun () -> Lwt.fail Exit)
+        (fun () -> raise Exit)
         (fun () -> raise Exception);
       Lwt.return_false
     with Exception ->
@@ -1404,7 +1413,7 @@ let backtrace_finalize_tests = suite "backtrace_finalize" [
     let p =
       Lwt.backtrace_finalize add_loc
         (fun () -> p)
-        (fun () -> Lwt.fail Exception)
+        (fun () -> raise Exception)
     in
     Lwt.wakeup r ();
     state_is (Lwt.Fail Exception) p
@@ -1439,7 +1448,7 @@ let backtrace_finalize_tests = suite "backtrace_finalize" [
     let p =
       Lwt.backtrace_finalize add_loc
         (fun () -> p)
-        (fun () -> Lwt.fail Exception)
+        (fun () -> raise Exception)
     in
     Lwt.wakeup_exn r Exit;
     state_is (Lwt.Fail Exception) p
@@ -1803,7 +1812,7 @@ let async_tests = suite "async" [
     let saw = ref None in
     let restore =
       set_async_exception_hook (fun exn -> saw := Some exn) in
-    Lwt.async (fun () -> Lwt.fail Exception);
+    Lwt.async (fun () -> raise Exception);
     later (fun () ->
       restore ();
       !saw = Some Exception)
@@ -1852,7 +1861,7 @@ let dont_wait_tests = suite "dont_wait" [
   test "rejected" begin fun () ->
     let saw = ref None in
     Lwt.dont_wait
-      (fun () -> Lwt.fail Exception)
+      (fun () -> raise Exception)
       (fun exn -> saw := Some exn);
     later (fun () -> !saw = Some Exception)
   end;
@@ -3371,7 +3380,7 @@ let cancel_catch_tests = suite "cancel catch" [
   test "task, pending, canceled, on_cancel, forwarded" begin fun () ->
     let on_cancel_2_ran = ref false in
     let p, _ = Lwt.task () in
-    let p' = Lwt.catch (fun () -> p) Lwt.fail in
+    let p' = Lwt.catch (fun () -> p) Lwt.reraise in
     Lwt.on_cancel p' (fun () -> on_cancel_2_ran := true);
     Lwt.cancel p';
     Lwt.return
@@ -3895,7 +3904,7 @@ let storage_tests = suite "storage" [
     Lwt.with_value key (Some 42) (fun () ->
       let p' =
         Lwt.with_value key (Some 1337) (fun () ->
-          Lwt.try_bind (fun () -> p) f Lwt.fail)
+          Lwt.try_bind (fun () -> p) f Lwt.reraise)
       in
       Lwt.wakeup r ();
       Lwt.return
diff --git a/test/core/test_lwt_pool.ml b/test/core/test_lwt_pool.ml
index cd7bf2706..942ca0d7e 100644
--- a/test/core/test_lwt_pool.ml
+++ b/test/core/test_lwt_pool.ml
@@ -16,7 +16,7 @@ let suite = suite "lwt_pool" [
   end;
 
   test "creator exception" begin fun () ->
-    let gen = fun () -> Lwt.fail Dummy_error in
+    let gen = fun () -> raise Dummy_error in
     let p = Lwt_pool.create 1 gen in
     let u = Lwt_pool.use p (fun _ -> Lwt.return 0) in
     Lwt.return (Lwt.state u = Lwt.Fail Dummy_error)
@@ -42,7 +42,7 @@ let suite = suite "lwt_pool" [
   test "validation exceptions are propagated to users" begin fun () ->
     let c = Lwt_condition.create () in
     let gen = (fun () -> let l = ref 0 in Lwt.return l) in
-    let v l = if !l = 0 then Lwt.return_true else Lwt.fail Dummy_error in
+    let v l = if !l = 0 then Lwt.return_true else raise Dummy_error in
     let p = Lwt_pool.create 1 ~validate:v gen in
     let u1 = Lwt_pool.use p (fun l -> l := 1; Lwt_condition.wait c) in
     let u2 = Lwt_pool.use p (fun l -> Lwt.return !l) in
@@ -106,7 +106,7 @@ let suite = suite "lwt_pool" [
   test "waiter are notified on replacement" begin fun () ->
     let c = Lwt_condition.create () in
     let gen = (fun () -> let l = ref 0 in Lwt.return l) in
-    let v l = if !l = 0 then Lwt.return_true else Lwt.fail Dummy_error in
+    let v l = if !l = 0 then Lwt.return_true else raise Dummy_error in
     let p = Lwt_pool.create 1 ~validate:v gen in
     let u1 = Lwt_pool.use p (fun l -> l := 1; Lwt_condition.wait c) in
     let u2 = Lwt_pool.use p (fun l -> Lwt.return !l) in
@@ -128,9 +128,9 @@ let suite = suite "lwt_pool" [
       if !k then
         let l = ref 0 in Lwt.return l
       else
-        Lwt.fail Dummy_error
+        raise Dummy_error
     in
-    let v l = if !l = 0 then Lwt.return_true else Lwt.fail Dummy_error in
+    let v l = if !l = 0 then Lwt.return_true else raise Dummy_error in
     let p = Lwt_pool.create 1 ~validate:v gen in
     let u1 = Lwt_pool.use p (fun l -> l := 1; k:= false; Lwt_condition.wait c) in
     let u2 = Lwt_pool.use p (fun l -> Lwt.return !l) in
@@ -156,7 +156,7 @@ let suite = suite "lwt_pool" [
     let cond = Lwt_condition.create() in
     let p = Lwt_pool.create 1 ~validate:v ~check:c gen in
     let _ = Lwt_pool.use p (fun l -> l := 1; Lwt_condition.wait cond) in
-    let _ = Lwt_pool.use p (fun l -> l := 2; Lwt.fail Dummy_error) in
+    let _ = Lwt_pool.use p (fun l -> l := 2; raise Dummy_error) in
     let u3 = Lwt_pool.use p (fun l -> Lwt.return !l) in
     let () = Lwt_condition.signal cond "done" in
     Lwt.bind u3 (fun v ->
@@ -169,7 +169,7 @@ let suite = suite "lwt_pool" [
     let p = Lwt_pool.create 1 gen in
     let _ = Lwt_pool.use p (fun l ->
       Lwt.bind (Lwt_condition.wait cond)
-        (fun _ -> l:= 1; Lwt.fail Dummy_error)) in
+        (fun _ -> l:= 1; raise Dummy_error)) in
     let u2 = Lwt_pool.use p (fun l -> Lwt.return !l) in
     let () = Lwt_condition.signal cond "done" in
     Lwt.bind u2 (fun v ->
diff --git a/test/core/test_lwt_result.ml b/test/core/test_lwt_result.ml
index 8e354b630..2f91ef5e6 100644
--- a/test/core/test_lwt_result.ml
+++ b/test/core/test_lwt_result.ml
@@ -93,7 +93,7 @@ let suite =
 
     test "catch, error case"
       (fun () ->
-         let x () = Lwt.fail Dummy_error in
+         let x () = raise Dummy_error in
          Lwt.return (Lwt_result.catch x = Lwt_result.fail Dummy_error)
       );
 
diff --git a/test/core/test_lwt_stream.ml b/test/core/test_lwt_stream.ml
index a19f0b3df..3e5193dc8 100644
--- a/test/core/test_lwt_stream.ml
+++ b/test/core/test_lwt_stream.ml
@@ -11,7 +11,7 @@ let expect_exit f =
       Lwt.return_false)
     (function
       | Exit -> Lwt.return_true
-      | e -> Lwt.fail e)
+      | e -> Lwt.reraise e)
 
 let suite = suite "lwt_stream" [
   test "from"
@@ -351,7 +351,7 @@ let suite = suite "lwt_stream" [
                     return (Some x)
                 | (Result.Error e)::l ->
                     q := l;
-                    Lwt.fail e)
+                    raise e)
        in
        Lwt_stream.to_list (Lwt_stream.wrap_exn stream) >>= fun l' ->
        return (l = l'));
@@ -418,7 +418,7 @@ let suite = suite "lwt_stream" [
 
   test "exception passing: basic, from"
     (fun () ->
-      let stream = Lwt_stream.from (fun () -> Lwt.fail Exit) in
+      let stream = Lwt_stream.from (fun () -> raise Exit) in
       expect_exit (fun () -> Lwt_stream.get stream));
 
   test "exception passing: basic, from_direct"
@@ -428,12 +428,12 @@ let suite = suite "lwt_stream" [
 
   test "exception passing: to_list"
     (fun () ->
-      let stream = Lwt_stream.from (fun () -> Lwt.fail Exit) in
+      let stream = Lwt_stream.from (fun () -> raise Exit) in
       expect_exit (fun () -> Lwt_stream.to_list stream));
 
   test "exception passing: mapped"
     (fun () ->
-      let stream = Lwt_stream.from (fun () -> Lwt.fail Exit) in
+      let stream = Lwt_stream.from (fun () -> raise Exit) in
       let stream = Lwt_stream.map (fun v -> v) stream in
       expect_exit (fun () -> Lwt_stream.get stream));
 
diff --git a/test/unix/test_lwt_bytes.ml b/test/unix/test_lwt_bytes.ml
index e29843ca8..6de438b8d 100644
--- a/test/unix/test_lwt_bytes.ml
+++ b/test/unix/test_lwt_bytes.ml
@@ -793,7 +793,7 @@ let suite = suite "lwt_bytes" [
         )
         (function
           | Invalid_argument _message -> Lwt.return_true
-          | exn -> Lwt.fail exn
+          | exn -> Lwt.reraise exn
         )
     end;
 
@@ -825,7 +825,7 @@ let suite = suite "lwt_bytes" [
         )
         (function
           | Invalid_argument _message -> Lwt.return_true
-          | exn -> Lwt.fail exn
+          | exn -> Lwt.reraise exn
         )
     end;
 
@@ -839,7 +839,7 @@ let suite = suite "lwt_bytes" [
         )
         (function
           | Invalid_argument _message -> Lwt.return_true
-          | exn -> Lwt.fail exn
+          | exn -> Lwt.reraise exn
         )
     end;
   ]
diff --git a/test/unix/test_lwt_engine.ml b/test/unix/test_lwt_engine.ml
index 38c7dcff1..3b6a5d231 100644
--- a/test/unix/test_lwt_engine.ml
+++ b/test/unix/test_lwt_engine.ml
@@ -49,7 +49,7 @@ let timing_tests = [
       | Lwt_unix.Timeout ->
         Lwt.return (Unix.gettimeofday ())
       | exn ->
-        Lwt.fail exn)
+        Lwt.reraise exn)
 
     >>= fun stop ->
 
diff --git a/test/unix/test_lwt_io.ml b/test/unix/test_lwt_io.ml
index f6bad19cd..f902f5e3e 100644
--- a/test/unix/test_lwt_io.ml
+++ b/test/unix/test_lwt_io.ml
@@ -320,7 +320,7 @@ let suite = suite "lwt_io" [
               exceptions_observed := !exceptions_observed + 1;
               Lwt.return_unit
             | exn ->
-              Lwt.fail exn) [@ocaml.warning "-4"]
+              Lwt.reraise exn) [@ocaml.warning "-4"]
       in
 
       let fd_r, fd_w = Lwt_unix.pipe () in
@@ -353,7 +353,7 @@ let suite = suite "lwt_io" [
       let filename = ref "." in
       let wrap f (filename', chan) = filename := filename'; f chan in
       let write_data chan = Lwt_io.write chan "test file content" in
-       let write_data_fail _ = Lwt.fail Dummy_error in
+      let write_data_fail _ = Lwt.fail Dummy_error in
       Lwt_io.with_temp_file (wrap write_data) ~prefix >>= fun _ ->
       let no_temps1 = not (Sys.file_exists !filename) in
        Lwt.catch
@@ -422,7 +422,7 @@ let suite = suite "lwt_io" [
       (function
       | Unix.Unix_error (Unix.EISDIR, "file_length", ".") ->
         Lwt.return_true
-      | exn -> Lwt.fail exn)
+      | exn -> Lwt.reraise exn)
   end;
 
   test "input channel of_bytes initial position"
diff --git a/test/unix/test_lwt_unix.ml b/test/unix/test_lwt_unix.ml
index b802d867d..609ca3c2a 100644
--- a/test/unix/test_lwt_unix.ml
+++ b/test/unix/test_lwt_unix.ml
@@ -172,7 +172,7 @@ let utimes_tests = [
         (function
         | Unix.Unix_error (Unix.ENOENT, "utimes", _) -> Lwt.return_unit
         | Unix.Unix_error (Unix.EUNKNOWNERR _, "utimes", _) -> Lwt.return_unit
-        | e -> Lwt.fail e) [@ocaml.warning "-4"] >>= fun () ->
+        | e -> Lwt.reraise e) [@ocaml.warning "-4"] >>= fun () ->
       Lwt.return_true);
 ]
 
@@ -218,7 +218,7 @@ let readdir_tests =
           Lwt.return (Some filename))
         (function
           | End_of_file -> Lwt.return_none
-          | exn -> Lwt.fail exn)
+          | exn -> Lwt.reraise exn)
       >>= function
         | None -> Lwt.return acc
         | Some filename -> loop (filename::acc)
@@ -305,7 +305,7 @@ let readdir_tests =
             (function
               | Unix.Unix_error (Unix.EBADF, tag', _) when tag' = tag ->
                 Lwt.return_true
-              | exn -> Lwt.fail exn) [@ocaml.warning "-4"]
+              | exn -> Lwt.reraise exn) [@ocaml.warning "-4"]
         in
 
         Lwt_list.for_all_s (fun (tag, t) -> expect_ebadf tag t)
@@ -711,7 +711,7 @@ let writev_tests =
                 Lwt.return_false)
               (function
                 | Invalid_argument _ -> Lwt.return_true
-                | e -> Lwt.fail e)
+                | e -> Lwt.reraise e)
         in
 
         let close write_fd = fun () ->
@@ -963,7 +963,7 @@ let bind_tests =
             | Unix.Unix_error (Unix.EADDRINUSE, "bind", _)
             | Unix.Unix_error (Unix.EISDIR, "bind", _) as exn ->
               if attempts <= 1 then
-                Lwt.fail exn
+                Lwt.reraise exn
               else
                 bind_loop (attempts - 1)
             | Unix.Unix_error (Unix.EPERM, "bind", _) ->
@@ -972,8 +972,8 @@ let bind_tests =
                  test should add a check for WSL by checking for the existence
                  of /proc/version, reading it, and checking its contents for the
                  string "WSL". *)
-              Lwt.fail Skip
-            | e -> Lwt.fail e) [@ocaml.warning "-4"]
+              raise Skip
+            | e -> Lwt.reraise e) [@ocaml.warning "-4"]
       in
 
       Lwt.finalize
@@ -1014,7 +1014,7 @@ let bind_tests =
           Lwt.return_false)
         (function
           | Unix.Unix_error (Unix.EBADF, _, _) -> Lwt.return_true
-          | e -> Lwt.fail e) [@ocaml.warning "-4"]);
+          | e -> Lwt.reraise e) [@ocaml.warning "-4"]);
 
   test "bind: aborted"
     (fun () ->
@@ -1028,7 +1028,7 @@ let bind_tests =
               Lwt.return_false)
             (function
               | Exit -> Lwt.return_true
-              | e -> Lwt.fail e))
+              | e -> Lwt.reraise e))
         (fun () -> Lwt_unix.close socket));
 ]
 
diff --git a/test/unix/test_mcast.ml b/test/unix/test_mcast.ml
index dbdfd446c..a44838f55 100644
--- a/test/unix/test_mcast.ml
+++ b/test/unix/test_mcast.ml
@@ -26,7 +26,7 @@ let child mcast_addr join fd =
   if debug then
     Printf.printf "\nReceived multicast message %S\n%!" (Bytes.unsafe_to_string (Bytes.sub buf 0 n));
   if Bytes.sub buf 0 n <> hello then
-    Lwt.fail (Failure "unexpected multicast message")
+    raise (Failure "unexpected multicast message")
   else
     Lwt.return_unit
 
@@ -61,9 +61,9 @@ let test_mcast name join set_loop =
           | Unix.Unix_error (Unix.EINVAL, "send", _)
           | Unix.Unix_error (Unix.ENODEV, "setsockopt", _)
           | Unix.Unix_error (Unix.ENETUNREACH, "send", _) ->
-            Lwt.fail Skip
+            raise Skip
           | e ->
-            Lwt.fail e
+            Lwt.reraise e
         )
     in
     Lwt.finalize t (fun () -> Lwt.join [Lwt_unix.close fd1; Lwt_unix.close fd2])
diff --git a/test/unix/test_sleep_and_timeout.ml b/test/unix/test_sleep_and_timeout.ml
index 40acf1385..70831ea57 100644
--- a/test/unix/test_sleep_and_timeout.ml
+++ b/test/unix/test_sleep_and_timeout.ml
@@ -35,7 +35,7 @@ let suite = suite "Lwt_unix sleep and timeout" [
           | Lwt_unix.Timeout ->
             let check = cmp_elapsed_time "timeout" start_time duration in
             Lwt.return check
-          | exn -> Lwt.fail exn
+          | exn -> Lwt.reraise exn
         )
     end;
 
@@ -61,7 +61,7 @@ let suite = suite "Lwt_unix sleep and timeout" [
             let check =
               cmp_elapsed_time "with_timeout : timeout" start_time duration in
             Lwt.return check
-          | exn -> Lwt.fail exn
+          | exn -> Lwt.reraise exn
         )
     end;