diff --git a/common b/common
index c423c60f5..39e23fc9a 160000
--- a/common
+++ b/common
@@ -1 +1 @@
-Subproject commit c423c60f502a189bb636ce1c669e15438ee89299
+Subproject commit 39e23fc9a7234e7a235efd49e6cdc21ae370ed93
diff --git a/include/villas/io.h b/include/villas/io.h
index 42bf0f81c..0a1f71aa0 100644
--- a/include/villas/io.h
+++ b/include/villas/io.h
@@ -138,7 +138,7 @@ int io_sscan(struct io *io, const char *buf, size_t len, size_t *rbytes, struct
  *
  * @param buf[out]	The buffer which should be filled with serialized data.
  * @param len[in]	The length of the buffer \p buf.
- * @param rbytes[out]	The number of bytes which have been written to \p buf. Ignored if NULL.
+ * @param rbytes[out]	The number of bytes which have been written to \p buf. Ignored if nullptr.
  * @param smps[in]	The array of pointers to samples.
  * @param cnt[in]	The number of pointers in the array \p smps.
  *
diff --git a/include/villas/memory.h b/include/villas/memory.h
index c69817ea5..a7d370dac 100644
--- a/include/villas/memory.h
+++ b/include/villas/memory.h
@@ -70,7 +70,7 @@ int memory_lock(size_t lock);
 
 /** Allocate \p len bytes memory of type \p m.
  *
- * @retval NULL If allocation failed.
+ * @retval nullptr If allocation failed.
  * @retval <>0  If allocation was successful.
  */
 void * memory_alloc(struct memory_type *m, size_t len);
diff --git a/include/villas/pool.h b/include/villas/pool.h
index df07aa037..259950080 100644
--- a/include/villas/pool.h
+++ b/include/villas/pool.h
@@ -83,7 +83,7 @@ INLINE ssize_t pool_put_many(struct pool *p, void *blocks[], size_t cnt)
 INLINE void * pool_get(struct pool *p)
 {
 	void *ptr;
-	return queue_pull(&p->queue, &ptr) == 1 ? ptr : NULL;
+	return queue_pull(&p->queue, &ptr) == 1 ? ptr : nullptr;
 }
 
 /** Release a memory block back to the pool. */
diff --git a/include/villas/sample.h b/include/villas/sample.h
index 5923b90d6..cde004c57 100644
--- a/include/villas/sample.h
+++ b/include/villas/sample.h
@@ -93,7 +93,7 @@ struct sample {
 #define SAMPLE_NON_POOL PTRDIFF_MIN
 
 /** Get the address of the pool to which the sample belongs. */
-#define sample_pool(s) ((s)->pool_off == SAMPLE_NON_POOL ? NULL : (struct pool *) ((char *) (s) + (s)->pool_off))
+#define sample_pool(s) ((s)->pool_off == SAMPLE_NON_POOL ? nullptr : (struct pool *) ((char *) (s) + (s)->pool_off))
 
 struct sample * sample_alloc(struct pool *p);
 
diff --git a/lib/formats/json.cpp b/lib/formats/json.cpp
index a0b53850b..1b75a0293 100644
--- a/lib/formats/json.cpp
+++ b/lib/formats/json.cpp
@@ -77,8 +77,8 @@ static int json_unpack_timestamps(json_t *json_ts, struct sample *smp)
 {
 	int ret;
 	json_error_t err;
-	json_t *json_ts_origin = NULL;
-	json_t *json_ts_received = NULL;
+	json_t *json_ts_origin = nullptr;
+	json_t *json_ts_received = nullptr;
 
 	json_unpack_ex(json_ts, &err, 0, "{ s?: o, s?: o }",
 		"origin",   &json_ts_origin,
@@ -185,7 +185,7 @@ static int json_unpack_sample(struct io *io, json_t *json_smp, struct sample *sm
 {
 	int ret;
 	json_error_t err;
-	json_t *json_data, *json_value, *json_ts = NULL;
+	json_t *json_data, *json_value, *json_ts = nullptr;
 	size_t i;
 	int64_t sequence = -1;
 
diff --git a/lib/formats/json_reserve.cpp b/lib/formats/json_reserve.cpp
index 2a51ec8df..1a98b8112 100644
--- a/lib/formats/json_reserve.cpp
+++ b/lib/formats/json_reserve.cpp
@@ -37,8 +37,8 @@ static int json_reserve_pack_sample(struct io *io, json_t **j, struct sample *sm
 {
 	json_error_t err;
 	json_t *json_data, *json_name, *json_unit, *json_value;
-	json_t *json_created = NULL;
-	json_t *json_sequence = NULL;
+	json_t *json_created = nullptr;
+	json_t *json_sequence = nullptr;
 
 	if (smp->flags & (int) SampleFlags::HAS_TS_ORIGIN)
 		json_created = json_integer(time_to_double(&smp->ts.origin) * 1e3);
@@ -67,7 +67,7 @@ static int json_reserve_pack_sample(struct io *io, json_t **j, struct sample *sm
 		if (sig->unit)
 			json_unit = json_string(sig->unit);
 		else
-			json_unit = NULL;
+			json_unit = nullptr;
 
 		json_value = json_pack_ex(&err, 0, "{ s: o, s: f }",
 			"name", json_name,
@@ -94,7 +94,7 @@ static int json_reserve_pack_sample(struct io *io, json_t **j, struct sample *sm
 	*j = json_pack_ex(&err, 0, "{ s: o }",
 		"measurements", json_data
 	);
-	if (*j == NULL)
+	if (*j == nullptr)
 		return -1;
 #if 0
 #ifdef JSON_RESERVE_INTEGER_TARGET
@@ -124,8 +124,8 @@ static int json_reserve_unpack_sample(struct io *io, json_t *json_smp, struct sa
 	int ret, idx;
 	double created = -1;
 	json_error_t err;
-	json_t *json_value, *json_data = NULL;
-	json_t *json_origin = NULL, *json_target = NULL;
+	json_t *json_value, *json_data = nullptr;
+	json_t *json_origin = nullptr, *json_target = nullptr;
 	size_t i;
 
 	ret = json_unpack_ex(json_smp, &err, 0, "{ s?: o, s?: o, s?: o, s?: o }",
@@ -173,7 +173,7 @@ static int json_reserve_unpack_sample(struct io *io, json_t *json_smp, struct sa
 	smp->length = 0;
 
 	json_array_foreach(json_data, i, json_value) {
-		const char *name, *unit = NULL;
+		const char *name, *unit = nullptr;
 		double value;
 
 		ret = json_unpack_ex(json_value, &err, 0, "{ s: s, s?: s, s: F, s?: F }",
diff --git a/lib/formats/protobuf.cpp b/lib/formats/protobuf.cpp
index eb83fc99a..2b764cd09 100644
--- a/lib/formats/protobuf.cpp
+++ b/lib/formats/protobuf.cpp
@@ -130,14 +130,14 @@ int protobuf_sprint(struct io *io, char *buf, size_t len, size_t *wbytes, struct
 		goto out;
 
 	villas__node__message__pack(pb_msg, (uint8_t *) buf);
-	villas__node__message__free_unpacked(pb_msg, NULL);
+	villas__node__message__free_unpacked(pb_msg, nullptr);
 
 	*wbytes = psz;
 
 	return cnt;
 
 out:
-	villas__node__message__free_unpacked(pb_msg, NULL);
+	villas__node__message__free_unpacked(pb_msg, nullptr);
 
 	return -1;
 }
@@ -147,7 +147,7 @@ int protobuf_sscan(struct io *io, const char *buf, size_t len, size_t *rbytes, s
 	unsigned i, j;
 	Villas__Node__Message *pb_msg;
 
-	pb_msg = villas__node__message__unpack(NULL, len, (uint8_t *) buf);
+	pb_msg = villas__node__message__unpack(nullptr, len, (uint8_t *) buf);
 	if (!pb_msg)
 		return -1;
 
@@ -218,7 +218,7 @@ int protobuf_sscan(struct io *io, const char *buf, size_t len, size_t *rbytes, s
 	if (rbytes)
 		*rbytes = villas__node__message__get_packed_size(pb_msg);
 
-	villas__node__message__free_unpacked(pb_msg, NULL);
+	villas__node__message__free_unpacked(pb_msg, nullptr);
 
 	return i;
 }