diff --git a/setup/mail-dovecot.sh b/setup/mail-dovecot.sh
index 734e7ed3..b146e44a 100755
--- a/setup/mail-dovecot.sh
+++ b/setup/mail-dovecot.sh
@@ -45,8 +45,8 @@ apt_install \
 # - https://www.dovecot.org/list/dovecot/2012-August/137569.html
 # - https://www.dovecot.org/list/dovecot/2011-December/132455.html
 tools/editconf.py /etc/dovecot/conf.d/10-master.conf \
-	default_process_limit="$(echo "$(nproc) * 250" | bc)" \
-	default_vsz_limit="$(echo "$(free -tm  | tail -1 | awk '{print $2}') / 3" | bc)M" \
+	default_process_limit="$(($(nproc) * 250))" \
+	default_vsz_limit="$(($(free -tm  | tail -1 | awk '{print $2}') / 3))M" \
 	log_path=/var/log/mail.log
 
 # The inotify `max_user_instances` default is 128, which constrains