ORA-01830: date format picture ends before converting entire input string I am trying to run the query on an Oracle database

select 
  to_date(trunc(sysdate) || '13:00:00','DD-MON-YY HH24:MI:SS') 
from dual;


and get the error   

ORA-01830: date format picture ends before converting entire input string


Please suggest.
SQL&gt; alter session set nls_Date_format = 'DD-MON-YY HH24:MI:SS';

Session altered.

SQL&gt; select trunc(sysdate, 'DD') + 13/24 from dual;

TRUNC(SYSDATE,'DD'
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29-AUG-15 13:00:00