[exim] Filter on plussign

I got at header that looks like this

X-SpamScore: +++++

i want to match it in my exim filter but i cant get it to work, i wont
match on the plussign

my filter looks like this for matching on s

# Exim filter
if $header_x-spamscore: matches "s{5,}" then
      finish
endif

Matches on 5 or more s's

This works perfectly, but i cant get it to work with plussign ala

# Exim filter
if $header_x-spamscore: matches "+{5,}" then
      finish
endif

Anyone got an idea?
--
Med venlig hilsen/Best regards
Lasse Birnbaum Jensen