accents/special chars in iframe

Hi,
How can I set UTF-8 for an iframe contained in the master page? (and before you start an argument about how bad iframes are or the difference between iframes and master pages have a look at this thread http://forums.asp.net/t/1948373.aspx?toggle+between+master+page+and+iframe+, the iframe is needed until all asp pages are converted to aspx.)
The problem is that all accent letters or other special chars are displayed with a black diamond with a question mark in it. And no, I don't need the option to change all these manually to html encoding like ä. It will not answer the question above.

Thanks for the help,
Pascal