[exim] delay with ratelimit

Hi,

I have updated to exim 4.60 for the use of the ratelimit condition. Reading
the spec.txt, I found this example:

# Slow down fast senders
warn
  ratelimit = 100 / 1h / per_rcpt / strict
  delay     = ${eval: $sender_rate - $sender_rate_limit }s

I can't get this working, because $sender_rate is not an integer but something
like 5.9, which does not work at my side:

exim -be '${eval:5.4-4}'
Failed: error in expression evaluation: expecting + or - (after processing
"5")

Is there any chance to get this working?
--
Thank you in advance.

Kerstin

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