diff --git a/back/srv/dashboard/add b/back/srv/dashboard/add
index 5a2f96a..2933d3f 100755
--- a/back/srv/dashboard/add
+++ b/back/srv/dashboard/add
@@ -74,7 +74,7 @@ used_ips="$(<<<"${ipv4s}" cut -d'.' -f3)\n$(<<<"${ipv6s}" cut -d'.' -f3)"
 used_hostnumbers="$(<<<"${used_ips}" sort | uniq)"
 hostnumber=1
 while printf '%s' "${used_hostnumbers}" | grep "${hostnumber}"
-	do hostnumber++
+	do ((hostnumber++))
 done
 ipv4="${IPV4_NET%.*.*}.${usernumber}.${hostnumber}"
 ipv6="${IPV6_NET%:*:*}:${usernumber}:${hostnumber}"