diff --git a/packer/ansible/roles/windowmanager/files/guest-account.sh b/packer/ansible/roles/windowmanager/files/guest-account.sh
index 968fa5c..bedde26 100644
--- a/packer/ansible/roles/windowmanager/files/guest-account.sh
+++ b/packer/ansible/roles/windowmanager/files/guest-account.sh
@@ -23,7 +23,7 @@ fi
 
 # read list of supplementary groups of the guest account from file
 if [ -f /etc/guest-account/groups ]; then
-  GROUPS="$(cat /etc/guest-account/groups)"
+  GROUPS="$(awk '{ if (NR==1) printf "%s", $0; else printf ",%s", $0; } END { print "" }' /etc/guest-account/groups)"
 fi
 
 is_system_user ()