SQL & PL/SQL

How to avoid ORA-19011: Character string buffer too small in below sql ?
create table xmltest (xmid number, xmdate date,xmcode number, xmdesc varchar2(100))

insert into xmltest
select level,sysdate + level,level*2 ,'Row'||level from dual connect by level <= 50

DECLARE
l_xml clob;
BEGIN
SELECT xmlagg(xmlelement("XMInfor"
                         ,xmlforest(TO_CHAR(a.xmdate, 'YYYYMMDD') AS "XMDATE"
                                   ,a.xmcode AS "XMCODE"
                                   ,a.xmdesc AS "XMDESC")
                         ,xmlcomment('  xmid->' || a.xmid))) || ''
  INTO l_xml
  FROM xmltest a;
              
END;