Using upper() / decode() together

I'm using postgres as the backend of a custom PHP Web application. Text
is base64_encode-d in php, then stored in varchar fields in postgres.

I'm trying to do this:
SELECT * from table where upper(decode(field,'base64')) like
upper('%sometext%');

I keep getting this error:
ERROR: function upper(bytea) does not exist
HINT: No function matches the given name and argument types. You may
need to add explicit type casts.

Is there any way to use upper in this manner?

--
Ross Gohlke
ross at grinz dot com