diff --git a/lib/oca_lib.ml b/lib/oca_lib.ml
index 0e73265..b709fe1 100644
--- a/lib/oca_lib.ml
+++ b/lib/oca_lib.ml
@@ -29,7 +29,7 @@ let get_files dirname =
         aux (file :: files)
     end begin function
     | End_of_file -> Lwt.return files
-    | exn -> Lwt.fail exn
+    | exn -> raise exn
     end
   in
   aux [] >>= fun files ->
@@ -66,12 +66,12 @@ let pread ?cwd ?exit1 ~timeout cmd f =
         | _, _ ->
             let cmd = String.concat " " cmd in
             prerr_endline ("Command '"^cmd^"' failed (exit status: "^string_of_int n^".");
-            Lwt.fail (Failure "process failure")
+            failwith "process failure"
         end
     | Unix.WSIGNALED n | Unix.WSTOPPED n ->
         let cmd = String.concat " " cmd in
         prerr_endline ("Command '"^cmd^"' killed by a signal (n°"^string_of_int n^")");
-        Lwt.fail (Failure "process failure")
+        failwith "process failure"
   end
 
 let read_unordered_lines c =
@@ -118,7 +118,7 @@ let mkdir_p dir =
           Lwt_unix.mkdir (Fpath.to_string dir) 0o750
         end begin function
         | Unix.Unix_error (Unix.EEXIST, _, _) -> Lwt.return_unit
-        | e -> Lwt.fail e
+        | e -> raise e
         end [@ocaml.warning "-fragile-match"] >>= fun () ->
         aux dir xs
   in
@@ -144,7 +144,7 @@ let rec rm_rf dirname =
     in
     Lwt.catch rm_files begin function
     | End_of_file -> Lwt.return_unit
-    | e -> Lwt.fail e
+    | e -> raise e
     end
   end begin fun () ->
     Lwt_unix.closedir dir >>= fun () ->
diff --git a/server/backend/admin.ml b/server/backend/admin.ml
index f96b288..80c594c 100644
--- a/server/backend/admin.ml
+++ b/server/backend/admin.ml
@@ -70,7 +70,7 @@ let admin_action ~on_finished ~conf ~run_trigger workdir body =
   | ["set-processes"; i] ->
       let i = int_of_string i in
       if i < 0 then
-        Lwt.fail_with "Cannot set the number of processes to a negative value."
+        failwith "Cannot set the number of processes to a negative value."
       else
         Server_configfile.set_processes conf i >|= fun () ->
         (fun () -> Lwt.return_none)
@@ -112,7 +112,7 @@ let admin_action ~on_finished ~conf ~run_trigger workdir body =
   | ["log"] ->
       get_log workdir
   | _ ->
-      Lwt.fail_with "Action unrecognized."
+      failwith "Action unrecognized."
   end >>= fun resp ->
   let stream = Lwt_stream.from resp in
   Cohttp_lwt_unix.Server.respond ~status:`OK ~body:(`Stream stream) ()
@@ -143,7 +143,7 @@ let callback ~on_finished ~conf ~run_trigger workdir _conn _req body =
   | Some (pversion, body) when String.equal Oca_lib.protocol_version pversion ->
       begin match String.Split.left ~by:"\n" body with
       | Some (_, "") ->
-          Lwt.fail_with "Empty message"
+          failwith "Empty message"
       | Some (user, body) ->
           get_user_key workdir user >>= fun key ->
           let body = decrypt key body in
@@ -151,12 +151,12 @@ let callback ~on_finished ~conf ~run_trigger workdir _conn _req body =
           | Some (user', body) when String.equal user user' ->
               admin_action ~on_finished ~conf ~run_trigger workdir body
           | Some _ ->
-              Lwt.fail_with "Identity couldn't be ensured"
+              failwith "Identity couldn't be ensured"
           | None ->
-              Lwt.fail_with "Identity check required"
+              failwith "Identity check required"
           end
       | None ->
-          Lwt.fail_with "Cannot find username"
+          failwith "Cannot find username"
       end
   | Some (pversion, _) ->
       Cohttp_lwt_unix.Server.respond_string
@@ -166,4 +166,4 @@ let callback ~on_finished ~conf ~run_trigger workdir _conn _req body =
                 Please upgrade your client.")
         ()
   | None ->
-      Lwt.fail_with "Cannot parse request"
+      failwith "Cannot parse request"
diff --git a/server/backend/check.ml b/server/backend/check.ml
index b42cb91..ec3200e 100644
--- a/server/backend/check.ml
+++ b/server/backend/check.ml
@@ -109,7 +109,7 @@ let ocluster_build_str ~debug ~cap ~conf ~base_obuilder ~stderr ~default c =
       Lwt.return r
   | (Error (), _) ->
       match default with
-      | None -> Lwt.fail_with ("Failure in ocluster: "^c) (* TODO: Replace this with "send message to debug slack webhook" *)
+      | None -> failwith ("Failure in ocluster: "^c) (* TODO: Replace this with "send message to debug slack webhook" *)
       | Some v -> Lwt.return v
 
 let failure_kind logfile =
@@ -410,7 +410,7 @@ let get_cap ~stderr ~cap_file =
       Lwt.return sr
   | Error _ ->
       Lwt_io.write_line stderr "cap file couldn't be loaded" >>= fun () ->
-      Lwt.fail_with "cap file not found"
+      failwith "cap file not found"
 
 let run_locked = ref false
 
diff --git a/server/lib/cache.ml b/server/lib/cache.ml
index add6dab..06ce730 100644
--- a/server/lib/cache.ml
+++ b/server/lib/cache.ml
@@ -195,7 +195,7 @@ let get_html ~conf self query logdir =
 
 let get_latest_logdir self =
   self.logdirs >>= function
-  | [] -> Lwt.fail Not_found
+  | [] -> raise Not_found
   | logdir::_ -> Lwt.return logdir
 
 let get_html ~conf self query logdir =
diff --git a/server/lib/server.ml b/server/lib/server.ml
index de1e59b..21b7cc8 100644
--- a/server/lib/server.ml
+++ b/server/lib/server.ml
@@ -122,7 +122,7 @@ module Make (Backend : Backend_intf.S) = struct
     (* TODO: Try to understand why it wouldn't do anything before when this was ~on_exn *)
     Lwt.catch
       (fun () -> callback ~conf backend conn req body)
-      (fun e -> if debug then prerr_endline (Printexc.get_backtrace () ^ Printexc.to_string e); Lwt.fail e)
+      (fun e -> if debug then prerr_endline (Printexc.get_backtrace () ^ Printexc.to_string e); raise e)
 
   let tcp_server port callback =
     Cohttp_lwt_unix.Server.create