User-defined functions in WHEN clause of a trigger

Hey all,

The subject says it all. In 8.1.7, can I:

	CREATE OR REPLACE TRIGGER my_trigger
	BEFORE UPDATE ON my_table
	FOR EACH ROW
	WHEN (my_function = 'SOME VALUE')
	BEGIN
		blah....
	END my_trigger;

Everytime I try to compile this, I get an "ORA-4076: invalid NEW or OLD specification". But I can specify a builtin function, e.g.:

        WHEN (SYS_CONTEXT('USERENV','HOST') = 'MYHOST') I've RTFM'd and tried Metalink as well, but I haven't been able to find anything that says I can't use a user-defined function here.

Anyone?

Rich Jesse                           System/Database Administrator
Rich.Jesse_at_qtiworld.com              Quad/Tech International, Sussex, WI USA