diff --git a/shadowsocks-libev.sh b/shadowsocks-libev.sh
index 3e36549..4406515 100644
--- a/shadowsocks-libev.sh
+++ b/shadowsocks-libev.sh
@@ -171,7 +171,7 @@ function firewall_set(){
     if centosversion 6; then
         /etc/init.d/iptables status > /dev/null 2>&1
         if [ $? -eq 0 ]; then
-            iptables -L -n | grep '${shadowsocksport}' > /dev/null 2>&1
+            iptables -L -n | grep -i ${shadowsocksport} > /dev/null 2>&1
             if [ $? -ne 0 ]; then
                 iptables -I INPUT -m state --state NEW -m tcp -p tcp --dport ${shadowsocksport} -j ACCEPT
                 iptables -I INPUT -m state --state NEW -m udp -p udp --dport ${shadowsocksport} -j ACCEPT