diff --git a/src/Firewall.cpp b/src/Firewall.cpp
index f94012c..6cf0fe0 100644
--- a/src/Firewall.cpp
+++ b/src/Firewall.cpp
@@ -58,6 +58,8 @@ namespace fw
     firewall_rule_t *Firewall::update_rule_of_firewall(String *args, const uint8_t key)
     {
         firewall_rule_t *rule_ptr = get_rule_from_firewall(key);
+        if (rule_ptr == NULL)
+            return rule_ptr;
         strncpy(rule_ptr->ip, args[IP].c_str(), sizeof(rule_ptr->ip));
         rule_ptr->port_from = args[PORT_FROM].toInt();
         rule_ptr->port_to = args[PORT_TO].toInt();