     pdu.command_id |> to_int
   end
 
-  @spec command_status(t) :: integer
+  @spec command_status(t) :: non_neg_integer
 
   @doc """
   Returns Pdu's `command_status`.

    pdu.command_status |> to_int
  end

  @spec sequence_number(t) :: integer

  @doc """
  Returns Pdu's `sequence_number`.

    end
  end

  @spec command_id(t) :: non_neg_integer

  @doc """
  Returns Pdu's `command_id`.
