diff --git a/inc/power.inc.sh b/inc/power.inc.sh
index 150009e9..c5e9bcc5 100644
--- a/inc/power.inc.sh
+++ b/inc/power.inc.sh
@@ -890,8 +890,8 @@ PDUCONTROL(){
 	
 		[ "${PORTSEL^^}" == "E" ] && exit 0
 		
-		tp=$(expr ${PORTSEL} - 1)
-		if [ "${PORTSEL}" != "" ] && [ "${PORT_DESC[${tp}]}" != "" ]; then
+		[ "${PORTSEL}" != "" ] && tp=$(expr ${PORTSEL} - 1)
+		if [ "${PORTSEL}" != "" ] && [[ "${PORTSEL}" =~ ^[0-9]+$ ]] && [ "${PORT_DESC[${tp}]}" != "" ]; then
 			portsel_power=$(snmpwalk -t 1 -r 0 -v 1 -c public ${PW_APCPDU_IP} .1.3.6.1.4.1.318.1.1.12.3.3.1.1.4.${PORTSEL} -O vq 2> /dev/null | sed -e 's/"//g')
 			[ ${portsel_power} -eq 1 ] && portsel_power_disp="${idsCL[Green]}ON" || portsel_power_disp="${idsCL[LightRed]}OFF"
 			[ ${portsel_power} -eq 2 ] && portsel_change_power_disp="${idsCL[Green]}ON" || portsel_change_power_disp="${idsCL[LightRed]}OFF"