rule creating infinite recursion not sure why

I was trying to create a rule to set a column to false whenever another
column was changed:

CREATE RULE...
ON UPDATE TO criterion
WHERE new.pattern::text <> old.pattern::text DO UPDATE table SET flag =
false
WHERE id = old.id

pattern | id
12345 | 1

=> update criterion set pattern = '12345' where id = 1;
ERROR: infinite recursion detected in rules for relation "criterion"

I'm not sure why it's detecting recursion in this case when the rule
conditional should be false

Thanks for any help...
gene