diff --git a/src/proto_alpha/lib_client_commands/client_proto_programs_commands.ml b/src/proto_alpha/lib_client_commands/client_proto_programs_commands.ml
index 0ca77d3f9..016ffde84 100644
--- a/src/proto_alpha/lib_client_commands/client_proto_programs_commands.ml
+++ b/src/proto_alpha/lib_client_commands/client_proto_programs_commands.ml
@@ -267,7 +267,7 @@ let commands () =
          begin
            if MBytes.get bytes 0 != '\005' then
              failwith "Not a piece of packed Michelson data (must start with `0x05`)"
-           else return ()
+           else return_unit
          end >>=? fun () ->
          (* Remove first byte *)
          let bytes = MBytes.sub bytes 1 ((MBytes.length bytes) - 1) in
diff --git a/src/proto_alpha/lib_delegate/client_baking_forge.ml b/src/proto_alpha/lib_delegate/client_baking_forge.ml
index 632e880fd..fd3f74de1 100644
--- a/src/proto_alpha/lib_delegate/client_baking_forge.ml
+++ b/src/proto_alpha/lib_delegate/client_baking_forge.ml
@@ -707,13 +707,12 @@ let shell_prevalidation
           f "Shell-side validation: error while prevalidating operations:@\n%a"
           -% t event "built_invalid_block_error"
           -% a errs_tag errs) >>= fun () ->
-      return None
+      return_none
   | Ok (shell_header, operations) ->
       let raw_ops =
         List.map (fun l ->
             List.map snd l.Preapply_result.applied) operations in
-      return
-        (Some (bi, priority, shell_header, raw_ops, delegate, seed_nonce_hash))
+      return_some (bi, priority, shell_header, raw_ops, delegate, seed_nonce_hash)
 
 let filter_outdated_endorsements expected_level ops =
   List.filter (function
@@ -934,7 +933,7 @@ let build_block
                 -% a timestamp_tag timestamp) >>= fun () ->
             finalize_block_header final_context ~timestamp validation_result operations >>=? fun shell_header ->
             let raw_ops = List.map (List.map forge) operations in
-            return (Some (bi, priority, shell_header, raw_ops, delegate, seed_nonce_hash))
+            return_some (bi, priority, shell_header, raw_ops, delegate, seed_nonce_hash)
 
 let previously_baked_level cctxt pkh new_lvl =
   State.get cctxt pkh  >>=? function
diff --git a/src/proto_alpha/lib_protocol/src/amendment.ml b/src/proto_alpha/lib_protocol/src/amendment.ml
index 75ad7c65e..af87c3b33 100644
--- a/src/proto_alpha/lib_protocol/src/amendment.ml
+++ b/src/proto_alpha/lib_protocol/src/amendment.ml
@@ -212,7 +212,7 @@ let rec longer_than l n =
 let record_proposals ctxt delegate proposals =
   begin match proposals with
     | [] -> fail Empty_proposal
-    | _ :: _ -> return ()
+    | _ :: _ -> return_unit
   end >>=? fun () ->
   Vote.get_current_period_kind ctxt >>=? function
   | Proposal ->
diff --git a/src/proto_alpha/lib_protocol/src/roll_storage.ml b/src/proto_alpha/lib_protocol/src/roll_storage.ml
index 0f1075f16..5e23d4ece 100644
--- a/src/proto_alpha/lib_protocol/src/roll_storage.ml
+++ b/src/proto_alpha/lib_protocol/src/roll_storage.ml
@@ -297,7 +297,7 @@ module Delegate = struct
       | None ->
           (* This case is only when called from `set_active`, when creating
              a contract. *)
-          return false
+          return_false
 
   let add_amount c delegate amount =
     ensure_inited c delegate >>=? fun c ->
diff --git a/src/proto_alpha/lib_protocol/src/script_ir_translator.ml b/src/proto_alpha/lib_protocol/src/script_ir_translator.ml
index d2e3d7b74..ad3a283df 100644
--- a/src/proto_alpha/lib_protocol/src/script_ir_translator.ml
+++ b/src/proto_alpha/lib_protocol/src/script_ir_translator.ml
@@ -1617,7 +1617,7 @@ and parse_instr
     let log_stack ctxt loc stack_ty aft =
       match type_logger, script_instr with
       | None, _
-      | Some _, (Seq (-1, _) | Int _ | String _ | Bytes _) -> return ()
+      | Some _, (Seq (-1, _) | Int _ | String _ | Bytes _) -> return_unit
       | Some log, (Prim _ | Seq _) ->
           (* Unparsing for logging done in an unlimited context as this
              is used only by the client and not the protocol *)
@@ -1625,7 +1625,7 @@ and parse_instr
           unparse_stack ctxt stack_ty >>=? fun (stack_ty, _) ->
           unparse_stack ctxt aft >>=? fun (aft, _) ->
           log loc stack_ty aft;
-          return ()
+          return_unit
     in
     let return :
       context -> bef judgement -> (bef judgement * context) tzresult Lwt.t = fun ctxt judgement ->
diff --git a/src/proto_alpha/lib_protocol/src/voting_services.ml b/src/proto_alpha/lib_protocol/src/voting_services.ml
index f4588caac..80a42a4cd 100644
--- a/src/proto_alpha/lib_protocol/src/voting_services.ml
+++ b/src/proto_alpha/lib_protocol/src/voting_services.ml
@@ -111,8 +111,8 @@ let register () =
   register0 S.current_proposal begin fun ctxt () () ->
     (* this would be better implemented using get_option in get_current_proposal *)
     Vote.get_current_proposal ctxt >>= function
-    | Ok p -> return (Some p)
-    | Error [Raw_context.Storage_error (Missing_key _)] -> return None
+    | Ok p -> return_some p
+    | Error [Raw_context.Storage_error (Missing_key _)] -> return_none
     | (Error _ as e) -> Lwt.return e
   end
 
diff --git a/src/proto_alpha/lib_protocol/test/transfer.ml b/src/proto_alpha/lib_protocol/test/transfer.ml
index c6a66e48b..cf30a1e85 100644
--- a/src/proto_alpha/lib_protocol/test/transfer.ml
+++ b/src/proto_alpha/lib_protocol/test/transfer.ml
@@ -557,7 +557,7 @@ let ownership_sender () =
   transfer_and_check_balances ~loc:__LOC__ b imcontract_1 contract_2 Tez.one
   >>=? fun (b,_) ->
   Incremental.finalize_block b >>=? fun _ ->
-  return ()
+  return_unit
 
 (*********************************************************************)
 (** Random transfer *)