diff --git a/src/plugin/ComponentManager.h b/src/plugin/ComponentManager.h
index 87d22fc189..c58db68765 100644
--- a/src/plugin/ComponentManager.h
+++ b/src/plugin/ComponentManager.h
@@ -134,7 +134,7 @@ ComponentManager<T, C>::ComponentManager(const string& arg_module, const string&
 	  tag_enum_type(make_intrusive<EnumType>(module + "::" + local_id))
 	{
 	auto id = install_ID(local_id.c_str(), module.c_str(), true, true);
-	add_type(id.get(), tag_enum_type, 0);
+	add_type(id.get(), tag_enum_type, nullptr);
 	zeekygen_mgr->Identifier(std::move(id));
 	}
 
diff --git a/src/plugin/Manager.cc b/src/plugin/Manager.cc
index 60be0212d7..09275e639f 100644
--- a/src/plugin/Manager.cc
+++ b/src/plugin/Manager.cc
@@ -19,9 +19,9 @@
 
 using namespace plugin;
 
-Plugin* Manager::current_plugin = 0;
-const char* Manager::current_dir = 0;
-const char* Manager::current_sopath = 0;
+Plugin* Manager::current_plugin = nullptr;
+const char* Manager::current_dir = nullptr;
+const char* Manager::current_sopath = nullptr;
 
 Manager::Manager()
 	{
@@ -29,7 +29,7 @@ Manager::Manager()
 	hooks = new hook_list*[NUM_HOOKS];
 
 	for ( int i = 0; i < NUM_HOOKS; i++ )
-		hooks[i] = 0;
+		hooks[i] = nullptr;
 	}
 
 Manager::~Manager()
@@ -238,7 +238,7 @@ bool Manager::ActivateDynamicPluginInternal(const std::string& name, bool ok_if_
 			{
 			const char* path = gl.gl_pathv[i];
 
-			current_plugin = 0;
+			current_plugin = nullptr;
 			current_dir = dir.c_str();
 			current_sopath = path;
 			void* hdl = dlopen(path, RTLD_LAZY | RTLD_GLOBAL);
@@ -270,9 +270,9 @@ bool Manager::ActivateDynamicPluginInternal(const std::string& name, bool ok_if_
 				reporter->FatalError("inconsistent plugin name: %s vs %s",
 						     current_plugin->Name().c_str(), name.c_str());
 
-			current_dir = 0;
-			current_sopath = 0;
-			current_plugin = 0;
+			current_dir = nullptr;
+			current_sopath = nullptr;
+			current_plugin = nullptr;
 
 			DBG_LOG(DBG_PLUGINS, "  Loaded %s", path);
 			}
@@ -461,7 +461,7 @@ Manager::inactive_plugin_list Manager::InactivePlugins() const
 
 Manager::plugin_list* Manager::ActivePluginsInternal()
 	{
-	static plugin_list* plugins = 0;
+	static plugin_list* plugins = nullptr;
 
 	if ( ! plugins )
 		plugins = new plugin_list;
@@ -471,7 +471,7 @@ Manager::plugin_list* Manager::ActivePluginsInternal()
 
 Manager::bif_init_func_map* Manager::BifFilesInternal()
 	{
-	static bif_init_func_map* bifs = 0;
+	static bif_init_func_map* bifs = nullptr;
 
 	if ( ! bifs )
 		bifs = new bif_init_func_map;
@@ -571,7 +571,7 @@ void Manager::DisableHook(HookType hook, Plugin* plugin)
 	if ( l->empty() )
 		{
 		delete l;
-		hooks[hook] = 0;
+		hooks[hook] = nullptr;
 		}
 	}
 
diff --git a/src/plugin/Manager.h b/src/plugin/Manager.h
index 25c0235ebf..9c0ffecad5 100644
--- a/src/plugin/Manager.h
+++ b/src/plugin/Manager.h
@@ -168,7 +168,7 @@ public:
 	bool HavePluginForHook(HookType hook) const
 		{
 		// Inline to avoid the function call.
-		return hooks[hook] != 0;
+		return hooks[hook] != nullptr;
 		}
 
 	/**
diff --git a/src/plugin/Plugin.cc b/src/plugin/Plugin.cc
index 29f177d329..5538b87b28 100644
--- a/src/plugin/Plugin.cc
+++ b/src/plugin/Plugin.cc
@@ -475,7 +475,7 @@ void Plugin::Describe(ODesc* d) const
 
 	for ( bif_item_list::const_iterator i = items.begin(); i != items.end(); i++ )
 		{
-		const char* type = 0;
+		const char* type = nullptr;
 
 		switch ( (*i).GetType() ) {
 		case BifItem::FUNCTION:
diff --git a/src/probabilistic/BloomFilter.cc b/src/probabilistic/BloomFilter.cc
index 71996dc6c8..e9289a9db9 100644
--- a/src/probabilistic/BloomFilter.cc
+++ b/src/probabilistic/BloomFilter.cc
@@ -17,7 +17,7 @@ using namespace probabilistic;
 
 BloomFilter::BloomFilter()
 	{
-	hasher = 0;
+	hasher = nullptr;
 	}
 
 BloomFilter::BloomFilter(const Hasher* arg_hasher)
@@ -142,7 +142,7 @@ std::string BasicBloomFilter::InternalState() const
 
 BasicBloomFilter::BasicBloomFilter()
 	{
-	bits = 0;
+	bits = nullptr;
 	}
 
 BasicBloomFilter::BasicBloomFilter(const Hasher* hasher, size_t cells)
@@ -195,7 +195,7 @@ bool BasicBloomFilter::DoUnserialize(const broker::data& data)
 
 CountingBloomFilter::CountingBloomFilter()
 	{
-	cells = 0;
+	cells = nullptr;
 	}
 
 CountingBloomFilter::CountingBloomFilter(const Hasher* hasher,
diff --git a/src/probabilistic/Topk.cc b/src/probabilistic/Topk.cc
index de3643a65d..fff53cbc1b 100644
--- a/src/probabilistic/Topk.cc
+++ b/src/probabilistic/Topk.cc
@@ -44,10 +44,10 @@ TopkVal::TopkVal(uint64_t arg_size) : OpaqueVal(topk_type)
 	elementDict = new PDict<Element>;
 	elementDict->SetDeleteFunc(topk_element_hash_delete_func);
 	size = arg_size;
-	type = 0;
+	type = nullptr;
 	numElements = 0;
 	pruned = false;
-	hash = 0;
+	hash = nullptr;
 	}
 
 TopkVal::TopkVal() : OpaqueVal(topk_type)
@@ -55,9 +55,9 @@ TopkVal::TopkVal() : OpaqueVal(topk_type)
 	elementDict = new PDict<Element>;
 	elementDict->SetDeleteFunc(topk_element_hash_delete_func);
 	size = 0;
-	type = 0;
+	type = nullptr;
 	numElements = 0;
-	hash = 0;
+	hash = nullptr;
 	}
 
 TopkVal::~TopkVal()
@@ -86,7 +86,7 @@ void TopkVal::Merge(const TopkVal* value, bool doPrune)
 		return;
 		}
 
-	if ( type == 0 )
+	if ( type == nullptr )
 		{
 		assert(numElements == 0);
 		Typify(value->type);
@@ -115,7 +115,7 @@ void TopkVal::Merge(const TopkVal* value, bool doPrune)
 			HashKey* key = GetHash(e->value);
 			Element* olde = (Element*) elementDict->Lookup(key);
 
-			if ( olde == 0 )
+			if ( olde == nullptr )
 				{
 				olde = new Element();
 				olde->epsilon = 0;
@@ -196,7 +196,7 @@ VectorVal* TopkVal::GetTopK(int k) const // returns vector
 	if ( numElements == 0 )
 		{
 		reporter->Error("Cannot return topk of empty");
-		return 0;
+		return nullptr;
 		}
 
 	auto vector_index = make_intrusive<TypeList>(IntrusivePtr{NewRef{}, type});
@@ -238,7 +238,7 @@ uint64_t TopkVal::GetCount(Val* value) const
 	Element* e = (Element*) elementDict->Lookup(key);
 	delete key;
 
-	if ( e == 0 )
+	if ( e == nullptr )
 		{
 		reporter->Error("GetCount for element that is not in top-k");
 		return 0;
@@ -253,7 +253,7 @@ uint64_t TopkVal::GetEpsilon(Val* value) const
 	Element* e = (Element*) elementDict->Lookup(key);
 	delete key;
 
-	if ( e == 0 )
+	if ( e == nullptr )
 		{
 		reporter->Error("GetEpsilon for element that is not in top-k");
 		return 0;
@@ -297,7 +297,7 @@ void TopkVal::Encountered(Val* encountered)
 	HashKey* key = GetHash(encountered);
 	Element* e = (Element*) elementDict->Lookup(key);
 
-	if ( e == 0 )
+	if ( e == nullptr )
 		{
 		e = new Element();
 		e->epsilon = 0;
@@ -370,7 +370,7 @@ void TopkVal::IncrementCounter(Element* e, unsigned int count)
 	// well, let's test if there is a bucket for currcount++
 	std::list<Bucket*>::iterator bucketIter = currBucket->bucketPos;
 
-	Bucket* nextBucket = 0;
+	Bucket* nextBucket = nullptr;
 
 	bucketIter++;
 
@@ -380,7 +380,7 @@ void TopkVal::IncrementCounter(Element* e, unsigned int count)
 	if ( bucketIter != buckets.end() && (*bucketIter)->count == currcount+count )
 		nextBucket = *bucketIter;
 
-	if ( nextBucket == 0 )
+	if ( nextBucket == nullptr )
 		{
 		// the bucket for the value that we want does not exist.
 		// create it...
@@ -405,7 +405,7 @@ void TopkVal::IncrementCounter(Element* e, unsigned int count)
 		{
 		buckets.remove(currBucket);
 		delete currBucket;
-		currBucket = 0;
+		currBucket = nullptr;
 		}
 	}
 
@@ -519,7 +519,7 @@ bool TopkVal::DoUnserialize(const broker::data& data)
 			b->elements.insert(b->elements.end(), e);
 
 			HashKey* key = GetHash(e->value);
-			assert (elementDict->Lookup(key) == 0);
+			assert (elementDict->Lookup(key) == nullptr);
 
 			elementDict->Insert(key, e);
 			delete key;
diff --git a/src/zeekygen/IdentifierInfo.h b/src/zeekygen/IdentifierInfo.h
index 949a503664..e21912d8fb 100644
--- a/src/zeekygen/IdentifierInfo.h
+++ b/src/zeekygen/IdentifierInfo.h
@@ -91,7 +91,7 @@ public:
 	 * comments are correctly associated.
 	 */
 	void CompletedTypeDecl()
-		{ last_field_seen = 0; }
+		{ last_field_seen = nullptr; }
 
 	/**
 	 * @return the script-level ID tracked by this info object.
diff --git a/src/zeekygen/Manager.cc b/src/zeekygen/Manager.cc
index b61cb15404..6636447516 100644
--- a/src/zeekygen/Manager.cc
+++ b/src/zeekygen/Manager.cc
@@ -288,7 +288,7 @@ void Manager::Identifier(IntrusivePtr<ID> id)
 			{
 			DBG_LOG(DBG_ZEEKYGEN, "Finished document for type %s", id->Name());
 			incomplete_type->CompletedTypeDecl();
-			incomplete_type = 0;
+			incomplete_type = nullptr;
 			return;
 			}
 
@@ -318,7 +318,7 @@ void Manager::Identifier(IntrusivePtr<ID> id)
 		// Handled specially since they don't have a script location.
 		DBG_LOG(DBG_ZEEKYGEN, "Made internal IdentifierInfo %s",
 		        id->Name());
-		CreateIdentifierInfo(id, 0);
+		CreateIdentifierInfo(id, nullptr);
 		return;
 		}
 
diff --git a/src/zeekygen/Target.cc b/src/zeekygen/Target.cc
index 34c3df6c9f..9aae9b82fe 100644
--- a/src/zeekygen/Target.cc
+++ b/src/zeekygen/Target.cc
@@ -438,7 +438,7 @@ vector<string> dir_contents_recursive(string dir)
 	char* dir_copy = copy_string(dir.c_str());
 	char** scan_path = new char*[2];
 	scan_path[0] = dir_copy;
-	scan_path[1] = 0;
+	scan_path[1] = NULL;
 
 	FTS* fts = fts_open(scan_path, FTS_NOCHDIR, 0);
 
diff --git a/src/zeekygen/Target.h b/src/zeekygen/Target.h
index 9aa95e58cf..2b8ae22c6d 100644
--- a/src/zeekygen/Target.h
+++ b/src/zeekygen/Target.h
@@ -148,7 +148,7 @@ public:
 		target_creator_map::const_iterator it = target_creators.find(type_name);
 
 		if ( it == target_creators.end() )
-			return 0;
+			return nullptr;
 
 		return it->second(name, pattern);
 		}