diff --git a/tpws/pools.c b/tpws/pools.c
index 32aa5ca..81a7b80 100644
--- a/tpws/pools.c
+++ b/tpws/pools.c
@@ -481,3 +481,9 @@ bool port_filters_in_range(const struct port_filters_head *head, uint16_t port)
 	}
 	return false;
 }
+bool port_filters_deny_if_empty(struct port_filters_head *head)
+{
+	port_filter pf;
+	if (LIST_FIRST(head)) return true;
+	return pf_parse("0",&pf) && port_filter_add(head,&pf);
+}
diff --git a/tpws/pools.h b/tpws/pools.h
index 5f23be4..cd37bdd 100644
--- a/tpws/pools.h
+++ b/tpws/pools.h
@@ -140,3 +140,4 @@ LIST_HEAD(port_filters_head, port_filter_item);
 bool port_filter_add(struct port_filters_head *head, const port_filter *pf);
 void port_filters_destroy(struct port_filters_head *head);
 bool port_filters_in_range(const struct port_filters_head *head, uint16_t port);
+bool port_filters_deny_if_empty(struct port_filters_head *head);