Tuple is to big

I have a little trouble with my PostgreSQL 6.5.1. I use a table with
text character type.
When I try to insert about 10000 character long string into it I've got
an error message like:
ERROR:  Tuple is too big: size 10172
Is there any limitation for a variable length text type?
If any, how long is it?

Regards,
Endre Bodoni