Using rownum with interval

Is there any limitation in passing dynamic values to INTERVAL?

SQL> select trunc(sysdate,'YY')+interval rownum year from dba_objects where rownum<9;
select trunc(sysdate,'YY')+interval rownum year from dba_objects where rownum<9
                                    *
ERROR at line 1:
ORA-00923: FROM keyword not found where expected

SQL> select trunc(sysdate,'YY')+interval '1' year from dba_objects where rownum<9;

TRUNC(SYS
---------
01-JAN-13
01-JAN-13
01-JAN-13
01-JAN-13
01-JAN-13
01-JAN-13
01-JAN-13
01-JAN-13

8 rows selected.

Thanks

Mukul