[Exim] Simple syntax error?

Hello.

I'm trying to get this to work in my exim.conf (exim 4.30):

# Add a "Quarantine" flag for spam scoring more than 6 but less than 8.
  warn  message = X-Spam-Quarantine: Yes
        spam = nobody:true
        condition = ${if >{$spam_score_int}{60}{${if
                                     <{$spam_score_int}{80}{1}{0}}}{0}}

(the condition line isn't really split over 2 lines, but this is an
email).

The problem is that whatever the spam score actually is, this condition
fails. Am I missing something really basic about the syntax of the
rules?

Oh, incidentally, this works:

        condition = ${if >{$spam_score_int}{60}{1}{0}}

but doesn't do what I want.

Thanks.

Paul.