diff --git a/firewall/firewall-add b/firewall/firewall-add
index 067e51a..d35f7c6 100755
--- a/firewall/firewall-add
+++ b/firewall/firewall-add
@@ -28,10 +28,10 @@ EXTRA_OPTIONS="$2 $3 $4"
       fi;
 
 
-if [[ $SOURCE_IP = "" ]]; then
+if [[ -z "$SOURCE_IP" ]]; then
 	SOURCE_IP="0.0.0.0/0"
 fi;
-if [[ $TARGET_IP = "" ]]; then
+if [[ -z "$TARGET_IP" ]]; then
 	TARGET_IP="0.0.0.0/0"
 fi;