diff --git a/lib/formats/csv.cpp b/lib/formats/csv.cpp
index 6b2c544f1..54fc5593a 100644
--- a/lib/formats/csv.cpp
+++ b/lib/formats/csv.cpp
@@ -110,7 +110,6 @@ static size_t csv_sscan_single(struct io *io, const char *buf, size_t len, struc
 	smp->flags |= (int) SampleFlags::HAS_SEQUENCE;
 
 	for (ptr = end + 1, i = 0; i < smp->capacity; ptr = end + 1, i++) {
-
 		if (*end == io->delimiter)
 			goto out;
 
@@ -177,7 +176,9 @@ void csv_header(struct io *io, const struct sample *smp)
 
 	if (io->flags & (int) SampleFlags::HAS_DATA) {
 		for (unsigned i = 0; i < smp->length; i++) {
-			struct signal *sig = (struct signal *) vlist_at(smp->signals, i);
+			struct signal *sig = (struct signal *) vlist_at_safe(smp->signals, i);
+			if (!sig)
+				break;
 
 			if (sig->name)
 				fprintf(f, "%s", sig->name);
diff --git a/lib/formats/json.cpp b/lib/formats/json.cpp
index 51b671de4..3141f4a5d 100644
--- a/lib/formats/json.cpp
+++ b/lib/formats/json.cpp
@@ -124,6 +124,8 @@ static int json_pack_sample(struct io *io, json_t **j, struct sample *smp)
 
 		for (unsigned i = 0; i < smp->length; i++) {
 			struct signal *sig = (struct signal *) vlist_at_safe(smp->signals, i);
+			if (!sig)
+				return -1;
 
 			json_t *json_value = signal_data_to_json(&smp->data[i], sig);
 
diff --git a/lib/formats/json_reserve.cpp b/lib/formats/json_reserve.cpp
index 3540f8c37..88767f42a 100644
--- a/lib/formats/json_reserve.cpp
+++ b/lib/formats/json_reserve.cpp
@@ -49,9 +49,7 @@ static int json_reserve_pack_sample(struct io *io, json_t **j, struct sample *sm
 	json_data = json_array();
 
 	for (unsigned i = 0; i < smp->length; i++) {
-		struct signal *sig;
-
-		sig = (struct signal *) vlist_at_safe(smp->signals, i);
+		struct signal *sig = (struct signal *) vlist_at_safe(smp->signals, i);
 		if (!sig)
 			return -1;
 
diff --git a/lib/formats/msg.cpp b/lib/formats/msg.cpp
index c2099639e..e9811a260 100644
--- a/lib/formats/msg.cpp
+++ b/lib/formats/msg.cpp
@@ -76,18 +76,17 @@ int msg_verify(struct msg *m)
 int msg_to_sample(struct msg *msg, struct sample *smp, struct vlist *signals)
 {
 	int ret;
+	unsigned i;
 
 	ret = msg_verify(msg);
 	if (ret)
-		return -1;
+		return ret;
 
-	smp->flags = (int) SampleFlags::HAS_TS_ORIGIN | (int) SampleFlags::HAS_SEQUENCE | (int) SampleFlags::HAS_DATA;
-	smp->length = MIN(msg->length, smp->capacity);
-	smp->sequence = msg->sequence;
-	MSG_TS(msg, smp->ts.origin);
-
-	for (unsigned i = 0; i < MIN(smp->length, vlist_length(signals)); i++) {
-		struct signal *sig = (struct signal *) vlist_at(signals, i);
+	unsigned len = MIN(msg->length, smp->capacity);
+	for (i = 0; i < MIN(len, vlist_length(signals)); i++) {
+		struct signal *sig = (struct signal *) vlist_at_safe(signals, i);
+		if (!sig)
+			return -1;
 
 		switch (sig->type) {
 			case SignalType::FLOAT:
@@ -103,6 +102,11 @@ int msg_to_sample(struct msg *msg, struct sample *smp, struct vlist *signals)
 		}
 	}
 
+	smp->flags = (int) SampleFlags::HAS_TS_ORIGIN | (int) SampleFlags::HAS_SEQUENCE | (int) SampleFlags::HAS_DATA;
+	smp->length = i;
+	smp->sequence = msg->sequence;
+	MSG_TS(msg, smp->ts.origin);
+
 	return 0;
 }
 
@@ -118,7 +122,9 @@ int msg_from_sample(struct msg *msg_in, struct sample *smp, struct vlist *signal
 	msg_in->ts.nsec = smp->ts.origin.tv_nsec;
 
 	for (unsigned i = 0; i < smp->length; i++) {
-		struct signal *sig = (struct signal *) vlist_at(signals, i);
+		struct signal *sig = (struct signal *) vlist_at_safe(signals, i);
+		if (!sig)
+			return -1;
 
 		switch (sig->type) {
 			case SignalType::FLOAT:
diff --git a/lib/formats/value.cpp b/lib/formats/value.cpp
index d6b625a3a..c9cb553fa 100644
--- a/lib/formats/value.cpp
+++ b/lib/formats/value.cpp
@@ -43,7 +43,7 @@ int value_sprint(struct io *io, char *buf, size_t len, size_t *wbytes, struct sa
 	for (i = 0; i < smp->length; i++) {
 		sig = (struct signal *) vlist_at_safe(smp->signals, i);
 		if (!sig)
-			break;
+			return -1;
 
 		off += signal_data_print_str(&smp->data[i], sig, buf, len);
 		off += snprintf(buf + off, len - off, "\n");
@@ -70,7 +70,7 @@ int value_sscan(struct io *io, const char *buf, size_t len, size_t *rbytes, stru
 	if (smp->capacity >= 1) {
 		struct signal *sig = (struct signal *) vlist_at_safe(io->signals, i);
 		if (!sig)
-			goto out;
+			return -1;
 
 		ret = signal_data_parse_str(&smp->data[i], sig, ptr, &end);
 		if (ret || end == ptr) /* There are no valid values anymore. */
diff --git a/lib/formats/villas_human.cpp b/lib/formats/villas_human.cpp
index 9cb60d6c9..90c3b01d3 100644
--- a/lib/formats/villas_human.cpp
+++ b/lib/formats/villas_human.cpp
@@ -133,7 +133,6 @@ static size_t villas_human_sscan_single(struct io *io, const char *buf, size_t l
 
 	unsigned i;
 	for (ptr = end + 1, i = 0; i < smp->capacity; ptr = end + 1, i++) {
-
 		if (*end == io->delimiter)
 			goto out;
 
@@ -208,7 +207,9 @@ void villas_human_header(struct io *io, const struct sample *smp)
 
 	if (io->flags & (int) SampleFlags::HAS_DATA) {
 		for (unsigned i = 0; i < MIN(smp->length, vlist_length(smp->signals)); i++) {
-			struct signal *sig = (struct signal *) vlist_at(smp->signals, i);
+			struct signal *sig = (struct signal *) vlist_at_safe(smp->signals, i);
+			if (!sig)
+				break;
 
 			if (sig->name)
 				fprintf(f, "%c%s", io->separator, sig->name);
diff --git a/lib/nodes/comedi.cpp b/lib/nodes/comedi.cpp
index f2422ddbf..72bc60519 100644
--- a/lib/nodes/comedi.cpp
+++ b/lib/nodes/comedi.cpp
@@ -579,6 +579,7 @@ int comedi_read(struct node *n, struct sample *smps[], unsigned cnt, unsigned *r
 			for (size_t i = 0; i < cnt; i++) {
 				d->counter++;
 
+				smps[i]->signals = &n->in.signals;
 				smps[i]->flags = (int) SampleFlags::HAS_TS_ORIGIN | (int) SampleFlags::HAS_DATA | (int) SampleFlags::HAS_SEQUENCE;
 				smps[i]->sequence = d->counter / d->chanlist_len;
 
diff --git a/lib/nodes/example.cpp b/lib/nodes/example.cpp
index 1fb80c836..e702a7257 100644
--- a/lib/nodes/example.cpp
+++ b/lib/nodes/example.cpp
@@ -179,6 +179,11 @@ int example_read(struct node *n, struct sample *smps[], unsigned cnt, unsigned *
 
 	smps[0]->data[0].f = time_delta(&now, &s->start_time);
 
+	/* Dont forget to set other flags in struct sample::flags
+	 * E.g. for sequence no, timestamps... */
+	smps[0]->flags = (int) SampleFlags::HAS_DATA;
+	smps[0]->signals = &n->in.signals;
+
 	read = 1; /* The number of samples read */
 
 	return read;
diff --git a/lib/nodes/fpga.cpp b/lib/nodes/fpga.cpp
index 509bd267e..4da9dc7ee 100644
--- a/lib/nodes/fpga.cpp
+++ b/lib/nodes/fpga.cpp
@@ -287,6 +287,8 @@ int fpga_read(struct node *n, struct sample *smps[], unsigned cnt, unsigned *rel
 	for (unsigned i = 0; i < MIN(read, smp->capacity); i++)
 		smp->data[i].i = f->in.mem[i];
 
+	smp->signals = &n->in.signals;
+
 	return read;
 }
 
diff --git a/lib/nodes/infiniband.cpp b/lib/nodes/infiniband.cpp
index dc17dbc5b..2ed97a39c 100644
--- a/lib/nodes/infiniband.cpp
+++ b/lib/nodes/infiniband.cpp
@@ -865,6 +865,7 @@ int ib_read(struct node *n, struct sample *smps[], unsigned cnt, unsigned *relea
 			smps[j]->length = SAMPLE_NUMBER_OF_VALUES(wc[j].byte_len - correction);
 			smps[j]->ts.received = ts_receive;
 			smps[j]->flags = (int) SampleFlags::HAS_TS_ORIGIN | (int) SampleFlags::HAS_TS_RECEIVED | (int) SampleFlags::HAS_SEQUENCE;
+			smps[j]->signals = &n->in.signals;
 		}
 
 	}
diff --git a/lib/nodes/ngsi.cpp b/lib/nodes/ngsi.cpp
index 916681059..f1ba80161 100644
--- a/lib/nodes/ngsi.cpp
+++ b/lib/nodes/ngsi.cpp
@@ -66,8 +66,10 @@ struct ngsi_response {
 	size_t len;
 };
 
-static json_t* ngsi_build_entity(struct ngsi *i, struct sample *smps[], unsigned cnt, int flags)
+static json_t* ngsi_build_entity(struct node *n, struct sample *smps[], unsigned cnt, int flags)
 {
+	struct ngsi *i = (struct ngsi *) n->_vd;
+
 	json_t *entity = json_pack("{ s: s, s: s, s: b }",
 		"id",		i->entity_id,
 		"type",		i->entity_type,
@@ -123,11 +125,13 @@ static json_t* ngsi_build_entity(struct ngsi *i, struct sample *smps[], unsigned
 	return entity;
 }
 
-static int ngsi_parse_entity(json_t *entity, struct ngsi *i, struct sample *smps[], unsigned cnt)
+static int ngsi_parse_entity(struct node *n, json_t *entity, struct sample *smps[], unsigned cnt)
 {
 	int ret;
 	const char *id, *name, *type;
 
+	struct ngsi *i = (struct ngsi *) n->_vd;
+
 	size_t l;
 	json_error_t err;
 	json_t *attribute, *attributes;
@@ -196,6 +200,8 @@ static int ngsi_parse_entity(json_t *entity, struct ngsi *i, struct sample *smps
 			smps[k]->data[map->index].f = strtof(value, &end);
 			if (value == end)
 				return -10;
+
+			smps[k]->signals = &n->in.signals;
 		}
 	}
 
@@ -503,7 +509,7 @@ int ngsi_start(struct node *n)
 	curl_easy_setopt(i->curl, CURLOPT_USERAGENT, USER_AGENT);
 
 	/* Create entity and atributes */
-	json_t *entity = ngsi_build_entity(i, nullptr, 0, NGSI_ENTITY_METADATA);
+	json_t *entity = ngsi_build_entity(n, nullptr, 0, NGSI_ENTITY_METADATA);
 
 	ret = ngsi_request_context_update(i->curl, i->endpoint, "APPEND", entity);
 	if (ret)
@@ -522,7 +528,7 @@ int ngsi_stop(struct node *n)
 	i->task.stop();
 
 	/* Delete complete entity (not just attributes) */
-	json_t *entity = ngsi_build_entity(i, nullptr, 0, 0);
+	json_t *entity = ngsi_build_entity(n, nullptr, 0, 0);
 
 	ret = ngsi_request_context_update(i->curl, i->endpoint, "DELETE", entity);
 
@@ -543,13 +549,13 @@ int ngsi_read(struct node *n, struct sample *smps[], unsigned cnt, unsigned *rel
 		perror("Failed to wait for task");
 
 	json_t *rentity;
-	json_t *entity = ngsi_build_entity(i, nullptr, 0, 0);
+	json_t *entity = ngsi_build_entity(n, nullptr, 0, 0);
 
 	ret = ngsi_request_context_query(i->curl, i->endpoint, entity, &rentity);
 	if (ret)
 		goto out;
 
-	ret = ngsi_parse_entity(rentity, i, smps, cnt);
+	ret = ngsi_parse_entity(n, entity, smps, cnt);
 	if (ret)
 		goto out2;
 
@@ -564,7 +570,7 @@ int ngsi_write(struct node *n, struct sample *smps[], unsigned cnt, unsigned *re
 	struct ngsi *i = (struct ngsi *) n->_vd;
 	int ret;
 
-	json_t *entity = ngsi_build_entity(i, smps, cnt, NGSI_ENTITY_VALUES);
+	json_t *entity = ngsi_build_entity(n, smps, cnt, NGSI_ENTITY_VALUES);
 
 	ret = ngsi_request_context_update(i->curl, i->endpoint, "UPDATE", entity);
 
diff --git a/lib/nodes/test_rtt.cpp b/lib/nodes/test_rtt.cpp
index b8de6188a..526a5cf98 100644
--- a/lib/nodes/test_rtt.cpp
+++ b/lib/nodes/test_rtt.cpp
@@ -399,6 +399,7 @@ int test_rtt_read(struct node *n, struct sample *smps[], unsigned cnt, unsigned
 			smps[i]->sequence = t->counter;
 			smps[i]->ts.origin = now;
 			smps[i]->flags = (int) SampleFlags::HAS_DATA | (int) SampleFlags::HAS_SEQUENCE | (int) SampleFlags::HAS_TS_ORIGIN;
+			smps[i]->signals = &n->in.signals;
 
 			t->counter++;
 		}