ORA-02065: illegal option for ALTER SYSTEM

In 10g database, when trying to change SGA_TARGET parameter in spfile, “ORA-02065: illegal option for ALTER SYSTEM” occurred.

$ sqlplus / as sysdba

SQL*Plus: Release 10.2.0.5.0 - Production on Tue Jun 13 15:56:37 2017
Copyright (c) 1982, 2010, Oracle. All Rights Reserved.
Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.5.0 - 64bit Production
With the Partitioning, Real Application Clusters, OLAP, Data Mining
and Real Application Testing options

SQL> show parameter sga_target

NAME_COL_PLUS_SHOW_PARAM TYPE        VALUE_COL_PLUS_SHOW_PARAM
------------------------ ----------- --------------------------
sga_target               big integer 4G

SQL> alter system set sga_target=2g sid='RACTEST1' scope=spfile;
 alter system set sga_target=2g sid='RACTEST1' scope=spfile
 *
ERROR at line 1:
ORA-02065: illegal option for ALTER SYSTEM

By swapping the order of “sid” and scope, it is working fine:

SQL> alter system set sga_target=2g scope=spfile sid='RACTEST1';

System altered.

SQL>