ORA-00068: invalid value while doing alter session set sort_area_size

I'm receiving below error while trying to alter sort_area_size with alter session.

However same command is working for another database. Need quick help on this please

DB - Oracle 11.2.0.4.0

SQL> alter session set sort_area_size=20000000;

ERROR:

ORA-00068: invalid value 20000000 for parameter sort_area_size, must be between

1208140597 and 186

Thanks,

Deepak