diff --git a/firewall/firewall-add b/firewall/firewall-add
index 785d3da..a015d1f 100755
--- a/firewall/firewall-add
+++ b/firewall/firewall-add
@@ -39,6 +39,17 @@ elif [[ "$(echo $SOURCE_IP | cut -d . -f4)" == "0" ]] ; then
 	SOURCE_IP="$SOURCE_IP/24";
 	debug "source ip is $SOURCE_IP"
 
+# Modifying source or target IP addresses if POSTROUTING rules needed to applied
+elif [[ ! -z "$POSTROUTING" ]]; then
+	if [[ ! -z "$SOURCE_IP" ]]; then
+	SOURCE_IP="$(echo $SOURCE_IP | cut -d . -f1-3).0/24";
+	debug "source ip is $SOURCE_IP"
+	fi
+	
+	if [[ ! -z "$TARGET_IP" ]]; then
+	TARGET_IP="$(echo $TARGET_IP | cut -d . -f1-3).0/24";
+	debug "target ip is $TARGET_IP"
+	fi
 fi;
 
 if [[ -z "$TARGET_IP" ]]; then