[exim] condition check in router with a space in the header

Hello!

I want to ask in a router if the Spam Flag is set to YES

condition = ${if def:h_X-Spam-FLAG: YES {1}{0}}

http://www.exim.org/exim-html-3.30/doc/html/filter_33.html

tells that it hat to be terminated with : if no whitespaces follow, but does
not tell how to get the above working.

if it remove modify it to
condition = ${if def:h_X-Spam-FLAG: {1}{0}}
it is working, but i want to ask in the router for YES and also for NO

I use exim 4.63.

Marco