diff --git a/lib/super_node.cpp b/lib/super_node.cpp
index cd1971120..538bb0368 100644
--- a/lib/super_node.cpp
+++ b/lib/super_node.cpp
@@ -192,15 +192,15 @@ int SuperNode::parseUri(const char *u)
 int SuperNode::parseJson(json_t *j)
 {
 	int ret;
-	const char *nme = NULL;
+	const char *nme = nullptr;
 
 	assert(state != STATE_STARTED);
 
-	json_t *json_nodes = NULL;
-	json_t *json_paths = NULL;
-	json_t *json_plugins = NULL;
-	json_t *json_logging = NULL;
-	json_t *json_web = NULL;
+	json_t *json_nodes = nullptr;
+	json_t *json_paths = nullptr;
+	json_t *json_plugins = nullptr;
+	json_t *json_logging = nullptr;
+	json_t *json_web = nullptr;
 
 	json_error_t err;
 
diff --git a/src/villas-convert.cpp b/src/villas-convert.cpp
index f102acf67..e7b2f45d0 100644
--- a/src/villas-convert.cpp
+++ b/src/villas-convert.cpp
@@ -117,7 +117,7 @@ check:		if (optarg == endptr)
 		if (ret)
 			error("Failed to validate IO configuration");
 
-		ret = io_open(dirs[i].io, NULL);
+		ret = io_open(dirs[i].io, nullptr);
 		if (ret)
 			error("Failed to open IO");
 	}
diff --git a/src/villas-hook.cpp b/src/villas-hook.cpp
index 2f040b09d..aa82b0eb0 100644
--- a/src/villas-hook.cpp
+++ b/src/villas-hook.cpp
@@ -209,7 +209,7 @@ check:		if (optarg == endptr)
 	if (ret)
 		error("Failed to validate IO configuration");
 
-	ret = io_open(&io, NULL);
+	ret = io_open(&io, nullptr);
 	if (ret)
 		error("Failed to open IO");
 
@@ -218,7 +218,7 @@ check:		if (optarg == endptr)
 	if (!ht)
 		error("Unknown hook function '%s'", hook);
 
-	ret = hook_init(&h, ht, NULL, NULL);
+	ret = hook_init(&h, ht, nullptr, nullptr);
 	if (ret)
 		error("Failed to initialize hook");
 
diff --git a/src/villas-node.cpp b/src/villas-node.cpp
index 5439f9597..ff48104d2 100644
--- a/src/villas-node.cpp
+++ b/src/villas-node.cpp
@@ -126,7 +126,7 @@ int main(int argc, char *argv[])
 		continue;
 	}
 
-	char *uri = argc == optind + 1 ? argv[optind] : NULL;
+	char *uri = argc == optind + 1 ? argv[optind] : nullptr;
 #endif /* ENABLE_OPAL_ASYNC */
 
 	info("This is VILLASnode %s (built on %s, %s)", CLR_BLD(CLR_YEL(PROJECT_BUILD_ID)),
diff --git a/src/villas-pipe.cpp b/src/villas-pipe.cpp
index e55fcc416..a987ce1f2 100644
--- a/src/villas-pipe.cpp
+++ b/src/villas-pipe.cpp
@@ -191,7 +191,7 @@ leave:	if (io_eof(&io)) {
 		killme(SIGTERM);
 	}
 
-	return NULL;
+	return nullptr;
 }
 
 static void * recv_loop(void *ctx)
@@ -235,7 +235,7 @@ static void * recv_loop(void *ctx)
 leave:	info("Reached receive limit. Terminating...");
 	killme(SIGTERM);
 
-	return NULL;
+	return nullptr;
 }
 
 int main(int argc, char *argv[])
@@ -334,7 +334,7 @@ check:		if (optarg == endptr)
 	if (ret)
 		error("Failed to validate IO configuration");
 
-	ret = io_open(&io, NULL);
+	ret = io_open(&io, nullptr);
 	if (ret)
 		error("Failed to open IO");
 
diff --git a/src/villas-signal.cpp b/src/villas-signal.cpp
index d8764531b..08613b06f 100644
--- a/src/villas-signal.cpp
+++ b/src/villas-signal.cpp
@@ -106,7 +106,7 @@ check:		if (optarg == endptr)
 	}
 
 	if (argc != optind + 1)
-		return NULL;
+		return nullptr;
 
 	type = argv[optind];
 
diff --git a/tests/unit/config_json.cpp b/tests/unit/config_json.cpp
index 9d282b4fb..55939451e 100644
--- a/tests/unit/config_json.cpp
+++ b/tests/unit/config_json.cpp
@@ -101,7 +101,7 @@ Test(utils, json_to_config)
 
 	cfg_root = config_root_setting(&cfg);
 
-	json = json_loads(json_example, 0, NULL);
+	json = json_loads(json_example, 0, nullptr);
 	cr_assert_not_null(json);
 
 	json_to_config(json, cfg_root);
diff --git a/tests/unit/json.cpp b/tests/unit/json.cpp
index 3600ca26e..375b69abc 100644
--- a/tests/unit/json.cpp
+++ b/tests/unit/json.cpp
@@ -37,37 +37,37 @@ ParameterizedTestParameters(json, json_load_cli)
 	static struct param params[] = {
 		// Combined long option
 		{
-			.argv = { "dummy", "--option=value", NULL },
+			.argv = { "dummy", "--option=value", nullptr },
 			.json = "{ \"option\" : \"value\" }"
 		},
 		// Separated long option
 		{
-			.argv = { "dummy", "--option", "value", NULL },
+			.argv = { "dummy", "--option", "value", nullptr },
 			.json = "{ \"option\" : \"value\" }"
 		},
 		// All kinds of data types
 		{
-			.argv = { "dummy", "--integer", "1", "--real", "1.1", "--bool", "true", "--null", "null", "--string", "hello world", NULL },
+			.argv = { "dummy", "--integer", "1", "--real", "1.1", "--bool", "true", "--null", "null", "--string", "hello world", nullptr },
 			.json = "{ \"integer\" : 1, \"real\" : 1.1, \"bool\" : true, \"null\" : null, \"string\" : \"hello world\" }"
 		},
 		// Array generation
 		{
-			.argv = { "dummy", "--bool", "true", "--bool", "false", NULL },
+			.argv = { "dummy", "--bool", "true", "--bool", "false", nullptr },
 			.json = "{ \"bool\" : [ true, false ] }"
 		},
 		// Dots in the option name generate sub objects
 		{
-			.argv = { "dummy", "--sub.option", "value", NULL },
+			.argv = { "dummy", "--sub.option", "value", nullptr },
 			.json = "{ \"sub\" : { \"option\" : \"value\" } }"
 		},
 		// Nesting is possible
 		{
-			.argv = { "dummy", "--sub.sub.option", "value", NULL },
+			.argv = { "dummy", "--sub.sub.option", "value", nullptr },
 			.json = "{ \"sub\" : { \"sub\" : { \"option\" : \"value\" } } }"
 		},
 		// Multiple subgroups are merged
 		{
-			.argv = { "dummy", "--sub.sub.option", "value1", "--sub.option", "value2", NULL },
+			.argv = { "dummy", "--sub.sub.option", "value1", "--sub.option", "value2", nullptr },
 			.json = "{ \"sub\" : { \"option\" : \"value2\", \"sub\" : { \"option\" : \"value1\" } } }"
 		}
 	};
diff --git a/tests/unit/mapping.cpp b/tests/unit/mapping.cpp
index 01d791fbd..9b999857d 100644
--- a/tests/unit/mapping.cpp
+++ b/tests/unit/mapping.cpp
@@ -54,7 +54,7 @@ Test(mapping, parse_nodes)
 		for (unsigned j = 0; j < ARRAY_LEN(signal_names[i]); j++) {
 			struct signal *sig;
 
-			sig = signal_create(signal_names[i][j], NULL, SIGNAL_TYPE_AUTO);
+			sig = signal_create(signal_names[i][j], nullptr, SIGNAL_TYPE_AUTO);
 			cr_assert_not_null(sig);
 
 			list_push(&n->signals, sig);
@@ -104,7 +104,7 @@ Test(mapping, parse_nodes)
 	cr_assert_eq(m.data.offset, 1);
 	cr_assert_eq(m.length, 2);
 
-	ret = list_destroy(&nodes, NULL, true);
+	ret = list_destroy(&nodes, nullptr, true);
 	cr_assert_eq(ret, 0);
 }
 
@@ -113,74 +113,74 @@ Test(mapping, parse)
 	int ret;
 	struct mapping_entry m;
 
-	ret = mapping_parse_str(&m, "ts.origin", NULL);
+	ret = mapping_parse_str(&m, "ts.origin", nullptr);
 	cr_assert_eq(ret, 0);
 	cr_assert_eq(m.type, MAPPING_TYPE_TIMESTAMP);
 	cr_assert_eq(m.timestamp.type, MAPPING_TIMESTAMP_TYPE_ORIGIN);
 
-	ret = mapping_parse_str(&m, "hdr.sequence", NULL);
+	ret = mapping_parse_str(&m, "hdr.sequence", nullptr);
 	cr_assert_eq(ret, 0);
 	cr_assert_eq(m.type, MAPPING_TYPE_HEADER);
 	cr_assert_eq(m.header.type, MAPPING_HEADER_TYPE_SEQUENCE);
 
-	ret = mapping_parse_str(&m, "stats.owd.mean", NULL);
+	ret = mapping_parse_str(&m, "stats.owd.mean", nullptr);
 	cr_assert_eq(ret, 0);
 	cr_assert_eq(m.type, MAPPING_TYPE_STATS);
 	cr_assert_eq(m.stats.id, STATS_OWD);
 	cr_assert_eq(m.stats.type, MAPPING_STATS_TYPE_MEAN);
 
-	ret = mapping_parse_str(&m, "data[1-2]", NULL);
+	ret = mapping_parse_str(&m, "data[1-2]", nullptr);
 	cr_assert_eq(ret, 0);
 	cr_assert_eq(m.type, MAPPING_TYPE_DATA);
 	cr_assert_eq(m.data.offset, 1);
 	cr_assert_eq(m.length, 2);
 
-	ret = mapping_parse_str(&m, "data[5-5]", NULL);
+	ret = mapping_parse_str(&m, "data[5-5]", nullptr);
 	cr_assert_eq(ret, 0);
 	cr_assert_eq(m.type, MAPPING_TYPE_DATA);
 	cr_assert_eq(m.data.offset, 5);
 	cr_assert_eq(m.length, 1);
 
-	ret = mapping_parse_str(&m, "data[22]", NULL);
+	ret = mapping_parse_str(&m, "data[22]", nullptr);
 	cr_assert_eq(ret, 0);
 	cr_assert_eq(m.type, MAPPING_TYPE_DATA);
 	cr_assert_eq(m.data.offset, 22);
 	cr_assert_eq(m.length, 1);
 
-	ret = mapping_parse_str(&m, "data", NULL);
+	ret = mapping_parse_str(&m, "data", nullptr);
 	cr_assert_eq(ret, 0);
 	cr_assert_eq(m.type, MAPPING_TYPE_DATA);
 	cr_assert_eq(m.data.offset, 0);
 	cr_assert_eq(m.length, 0);
 
-	ret = mapping_parse_str(&m, "data[]", NULL);
+	ret = mapping_parse_str(&m, "data[]", nullptr);
 	cr_assert_eq(ret, 0);
 	cr_assert_eq(m.type, MAPPING_TYPE_DATA);
 	cr_assert_eq(m.data.offset, 0);
 	cr_assert_eq(m.length, 0);
 
-	ret = mapping_parse_str(&m, "data[1.1-2f]", NULL);
+	ret = mapping_parse_str(&m, "data[1.1-2f]", nullptr);
 	cr_assert_neq(ret, 0);
 
 	/* Missing parts */
-	ret = mapping_parse_str(&m, "stats.owd", NULL);
+	ret = mapping_parse_str(&m, "stats.owd", nullptr);
 	cr_assert_neq(ret, 0);
 
 	/* This a type */
-	ret = mapping_parse_str(&m, "hdr.sequences", NULL);
+	ret = mapping_parse_str(&m, "hdr.sequences", nullptr);
 	cr_assert_neq(ret, 0);
 
 	/* Check for superfluous chars at the end */
-	ret = mapping_parse_str(&m, "stats.ts.origin.bla", NULL);
+	ret = mapping_parse_str(&m, "stats.ts.origin.bla", nullptr);
 	cr_assert_neq(ret, 0);
 
-	ret = mapping_parse_str(&m, "stats.ts.origin.", NULL);
+	ret = mapping_parse_str(&m, "stats.ts.origin.", nullptr);
 	cr_assert_neq(ret, 0);
 
-	ret = mapping_parse_str(&m, "data[1-2]bla", NULL);
+	ret = mapping_parse_str(&m, "data[1-2]bla", nullptr);
 	cr_assert_neq(ret, 0);
 
 	/* Negative length of chunk */
-	ret = mapping_parse_str(&m, "data[5-3]", NULL);
+	ret = mapping_parse_str(&m, "data[5-3]", nullptr);
 	cr_assert_eq(ret, -1);
 }
diff --git a/tests/unit/pool.cpp b/tests/unit/pool.cpp
index 35a82acee..14abc9414 100644
--- a/tests/unit/pool.cpp
+++ b/tests/unit/pool.cpp
@@ -62,7 +62,7 @@ ParameterizedTest(struct param *p, pool, basic, .init = init_memory)
 	cr_assert_eq(ret, 0, "Failed to create pool");
 
 	ptr = pool_get(&pool);
-	cr_assert_neq(ptr, NULL);
+	cr_assert_neq(ptr, nullptr);
 
 	memset(ptr, 1, p->block_size); /* check that we dont get a seg fault */
 
@@ -70,15 +70,15 @@ ParameterizedTest(struct param *p, pool, basic, .init = init_memory)
 	for (i = 1; i < p->pool_size; i++) {
 		ptrs[i] = pool_get(&pool);
 
-		if (ptrs[i] == NULL)
+		if (ptrs[i] == nullptr)
 			break;
 	}
 
 	if (i < p->pool_size)
-		cr_assert_neq(ptrs[i], NULL);
+		cr_assert_neq(ptrs[i], nullptr);
 
 	ptr = pool_get(&pool);
-	cr_assert_eq(ptr, NULL);
+	cr_assert_eq(ptr, nullptr);
 
 	ret = pool_destroy(&pool);
 	cr_assert_eq(ret, 0, "Failed to destroy pool");
diff --git a/tests/unit/queue.cpp b/tests/unit/queue.cpp
index d3f79b47b..5128a637d 100644
--- a/tests/unit/queue.cpp
+++ b/tests/unit/queue.cpp
@@ -117,7 +117,7 @@ static void * producer(void *ctx)
 
 	//cr_log_info("producer: finished");
 
-	return NULL;
+	return nullptr;
 }
 
 static void * consumer(void *ctx)
@@ -157,7 +157,7 @@ static void * consumer(void *ctx)
 
 	//cr_log_info("consumer: finished");
 
-	return NULL;
+	return nullptr;
 }
 
 #if defined(_POSIX_BARRIERS) && _POSIX_BARRIERS > 0
@@ -319,14 +319,13 @@ ParameterizedTest(struct param *p, queue, multi_threaded, .timeout = 20, .init =
 
 	uint64_t start_tsc_time, end_tsc_time;
 
-	pthread_barrier_init(&barrier, NULL, p->thread_count);
+	pthread_barrier_init(&barrier, nullptr, p->thread_count);
 
 	for (int i = 0; i < p->thread_count; ++i)
-		pthread_create(&threads[i], NULL, p->many ? producer_consumer_many : producer_consumer, p);
+		pthread_create(&threads[i], nullptr, p->many ? producer_consumer_many : producer_consumer, p);
 
 	sleep(0.2);
 
-
 	ret = tsc_init(&tsc);
 	cr_assert(!ret);
 
@@ -334,7 +333,7 @@ ParameterizedTest(struct param *p, queue, multi_threaded, .timeout = 20, .init =
 	p->start = 1;
 
 	for (int i = 0; i < p->thread_count; ++i)
-		pthread_join(threads[i], NULL);
+		pthread_join(threads[i], nullptr);
 
 	end_tsc_time = tsc_now(&tsc);
 	cycpop = (end_tsc_time - start_tsc_time) / p->iter_count;
diff --git a/tests/unit/queue_signalled.cpp b/tests/unit/queue_signalled.cpp
index 1b47c9931..ab1127425 100644
--- a/tests/unit/queue_signalled.cpp
+++ b/tests/unit/queue_signalled.cpp
@@ -52,7 +52,7 @@ static void * producer(void * ctx)
 		usleep(0.1e-3 * 1e6); /* 1 ms */
 	}
 
-	return NULL;
+	return nullptr;
 }
 
 static void * consumer(void * ctx)
@@ -73,7 +73,7 @@ static void * consumer(void * ctx)
 		}
 	}
 
-	return NULL;
+	return nullptr;
 }
 
  void * polled_consumer(void *ctx)
@@ -106,7 +106,7 @@ again:		ret = poll(&pfd, 1, -1);
 			return (void *) 2; /* Indicates an error to the parent thread */
 	}
 
-	return NULL;
+	return nullptr;
 }
 
 ParameterizedTestParameters(queue_signalled, simple)
@@ -138,10 +138,10 @@ ParameterizedTest(struct param *param, queue_signalled, simple, .timeout = 5, .i
 	ret = queue_signalled_init(&q, LOG2_CEIL(NUM_ELEM), &memory_heap, param->flags);
 	cr_assert_eq(ret, 0, "Failed to initialize queue: flags=%#x, ret=%d", param->flags, ret);
 
-	ret = pthread_create(&t1, NULL, producer, &q);
+	ret = pthread_create(&t1, nullptr, producer, &q);
 	cr_assert_eq(ret, 0);
 
-	ret = pthread_create(&t2, NULL, param->polled ? polled_consumer : consumer, &q);
+	ret = pthread_create(&t2, nullptr, param->polled ? polled_consumer : consumer, &q);
 	cr_assert_eq(ret, 0);
 
 	ret = pthread_join(t1, &r1);