SQL & PL/SQL

i have a two tables with following columns

DOCUMENTNO | DOCDATE | SERIAL (table_name=MASTER).
ITEMCODE | DEPARTMENT | QUANTITY | SERIAL (table_name=DETAIL).

here MASTER.SERIAL=DETAIL.SERIAL

the table named MASTER contains only one record against one SERIAL.
but the table name DETAIL can contain many records against one SERIAL.

a cursor selects DOCUMENTNO from MASTER table and stores it into a variable V_DCNO.
now the main command comes which sometimes got the issue.

select MASTER.DOCDATE,DETAIL.DEPARTMENT into V_DCDATE,V_DEPTNO from MASTER,DETAIL
where MASTER.SERIAL=DETAIL.SERIAL and MASTER.DOCUMENTNO=V_DCNO AND DETAIL.ITEMCODE=V_ITMCOD;

now the upper command will return more then one rows if DEPARTMENT is more then one in one document against V_ITMCOD.

in such case variables cant hold double information of two rows. and it raises ORA-01402.

how to solve this problem please help?