diff --git a/setup/web.sh b/setup/web.sh
index 089de290..d1fe6a32 100755
--- a/setup/web.sh
+++ b/setup/web.sh
@@ -126,7 +126,7 @@ chmod a+r /var/lib/mailinabox/mozilla-autoconfig.xml
 # nginx configuration at /.well-known/mta-sts.txt
 # more documentation is available on: 
 # https://www.uriports.com/blog/mta-sts-explained/
-
+PUNY_PRIMARY_HOSTNAME=$(echo "$PRIMARY_HOSTNAME" | idn2)
 cat conf/mta-sts.txt \
         | sed "s/MODE/$MTA_STS/" \
         | sed "s/PRIMARY_HOSTNAME/$PUNY_PRIMARY_HOSTNAME/" \