diff --git a/src/proto_alpha/lib_client/client_proto_args.ml b/src/proto_alpha/lib_client/client_proto_args.ml
index ec039eb8b..439bb57b3 100644
--- a/src/proto_alpha/lib_client/client_proto_args.ml
+++ b/src/proto_alpha/lib_client/client_proto_args.ml
@@ -89,11 +89,10 @@ let init_arg =
     string_parameter
 
 let arg_arg =
-  default_arg
+  arg
     ~long:"arg"
     ~placeholder:"data"
     ~doc:"argument passed to the contract's script, if needed"
-    ~default:"Unit"
     string_parameter
 
 let delegate_arg =
diff --git a/src/proto_alpha/lib_client/client_proto_args.mli b/src/proto_alpha/lib_client/client_proto_args.mli
index ed669660f..115933e2e 100644
--- a/src/proto_alpha/lib_client/client_proto_args.mli
+++ b/src/proto_alpha/lib_client/client_proto_args.mli
@@ -16,7 +16,7 @@ val init_arg: (string, Proto_alpha.full) Clic.arg
 val fee_arg: (Tez.t, Proto_alpha.full) Clic.arg
 val gas_limit_arg: (Z.t option, Proto_alpha.full) Clic.arg
 val storage_limit_arg: (Z.t option, Proto_alpha.full) Clic.arg
-val arg_arg: (string, Proto_alpha.full) Clic.arg
+val arg_arg: (string option, Proto_alpha.full) Clic.arg
 val source_arg: (string option, Proto_alpha.full) Clic.arg
 
 val delegate_arg: (Signature.Public_key_hash.t option, Proto_alpha.full) Clic.arg
diff --git a/src/proto_alpha/lib_client_commands/client_proto_context_commands.ml b/src/proto_alpha/lib_client_commands/client_proto_context_commands.ml
index 63966bc53..6d768b678 100644
--- a/src/proto_alpha/lib_client_commands/client_proto_context_commands.ml
+++ b/src/proto_alpha/lib_client_commands/client_proto_context_commands.ml
@@ -304,7 +304,7 @@ let commands () =
         transfer cctxt
           ~chain:`Main ~block:cctxt#block ?confirmations:cctxt#confirmations
           ~dry_run
-          ~source ~fee ~src_pk ~src_sk ~destination ~arg ~amount ?gas_limit ?storage_limit () >>=
+          ~source ~fee ~src_pk ~src_sk ~destination ?arg ~amount ?gas_limit ?storage_limit () >>=
         report_michelson_errors ~no_print_source ~msg:"transfer simulation failed" cctxt >>= function
         | None -> return_unit
         | Some (_res, _contracts) ->