diff --git a/src/dnslib/node.c b/src/dnslib/node.c
index 2c11ec284e6bb238f35cdc75c0e9eec62f2d2aa4..7000463c1a838a2fe6bcacbad1bb18a35d2b9b0a 100644
--- a/src/dnslib/node.c
+++ b/src/dnslib/node.c
@@ -293,6 +293,13 @@ int dnslib_node_is_non_auth(const dnslib_node_t *node)
 
 /*----------------------------------------------------------------------------*/
 
+int dnslib_node_is_auth(const dnslib_node_t *node)
+{
+	return (node->flags == 0);
+}
+
+/*----------------------------------------------------------------------------*/
+
 void dnslib_node_free_rrsets(dnslib_node_t *node, int free_rdata_dnames)
 {
 	skip_node_t *skip_node =
diff --git a/src/dnslib/node.h b/src/dnslib/node.h
index d9e66f683c87dfd8deefb7b2eb9fc9503d96eeba..456e48cf2a738258d25df0cf19e2756d0e2ea248 100644
--- a/src/dnslib/node.h
+++ b/src/dnslib/node.h
@@ -263,6 +263,8 @@ void dnslib_node_set_non_auth(dnslib_node_t *node);
  */
 int dnslib_node_is_non_auth(const dnslib_node_t *node);
 
+int dnslib_node_is_auth(const dnslib_node_t *node);
+
 /*!
  * \brief Destroys the RRSets within the node structure.
  *
diff --git a/src/knot/server/name-server.c b/src/knot/server/name-server.c
index a0125e18eb9982133d7ec9c5f23b60d6cc7bdb80..c56455e18041e588633ea1f6bc9604dd9d387f35 100644
--- a/src/knot/server/name-server.c
+++ b/src/knot/server/name-server.c
@@ -162,6 +162,11 @@ static dnslib_rrset_t *ns_synth_from_wildcard(
 static void ns_check_wildcard(const dnslib_dname_t *name, dnslib_packet_t *resp,
                               const dnslib_rrset_t **rrset)
 {
+	assert(name != NULL);
+	assert(resp != NULL);
+	assert(rrset != NULL);
+	assert(*rrset != NULL);
+
 	if (dnslib_dname_is_wildcard((*rrset)->owner)) {
 		dnslib_rrset_t *synth_rrset =
 			ns_synth_from_wildcard(*rrset, name);
@@ -357,6 +362,11 @@ DEBUG_NS(
 			assert(rrsets[i] != NULL);
 			rrset = dnslib_rrset_rrsigs(rrsets[i]);
 
+			if (rrset == NULL) {
+				++i;
+				continue;
+			}
+
 			ns_check_wildcard(name, resp, &rrset);
 			ret = dnslib_response2_add_rrset_answer(resp, rrset, 1,
 			                                        0, 0);