SET CONSTRAINTS in procedure results in ORA-922

 Hi all.  Am running Oracle Enterprise Edition, 11.2.0.2.  Am trying to defer constraint validation inside a procedure, but the command to do so isn't recognized.  Is there something I'm missing?

Here's a quick-n-dirty sample:

create or replace package bob_test is

    procedure cons_test;

end bob_test;

/

create or replace package body bob_test is

    procedure cons_test is

        cnt number;

    begin

        set constraints all deferred;

        select count(*) into cnt from dual;

    end cons_test;

end bob_test;

/

show errors

When I attempt to run this I get the following:

Errors for PACKAGE BODY BOB_TEST:

LINE/COL ERROR

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