diff --git a/dnsapi/dns_limacity.sh b/dnsapi/dns_limacity.sh
index 6719b405..d7d5223d 100644
--- a/dnsapi/dns_limacity.sh
+++ b/dnsapi/dns_limacity.sh
@@ -63,7 +63,7 @@ _lima_get_root() {
   _lima_get_root=$1
   i=1
   while true; do
-    h=$(printf "%s" "$_lima_get_root" | cut -d . -f $i-100)
+    h=$(printf "%s" "$_lima_get_root" | cut -d . -f $(_math "$i" -100))
     _debug h "$h"
     if [ -z "$h" ]; then
       #not valid