diff --git a/examples/client_test.cpp b/examples/client_test.cpp
index c1ebd9a7a..65d1fda7b 100644
--- a/examples/client_test.cpp
+++ b/examples/client_test.cpp
@@ -354,7 +354,7 @@ std::string print_endpoint(libtorrent::tcp::endpoint const& ep)
 
 struct torrent_entry
 {
-	torrent_entry(libtorrent::torrent_handle h) : handle(std::move(h)) {}
+	explicit torrent_entry(libtorrent::torrent_handle h) : handle(std::move(h)) {}
 	libtorrent::torrent_handle handle;
 	libtorrent::torrent_status status;
 };
diff --git a/simulation/setup_dht.cpp b/simulation/setup_dht.cpp
index fa5b57a59..9563d5561 100644
--- a/simulation/setup_dht.cpp
+++ b/simulation/setup_dht.cpp
@@ -302,7 +302,7 @@ dht_network::dht_network(sim::simulation& sim, int num_nodes, std::uint32_t flag
 	}
 }
 
-dht_network::~dht_network() {}
+dht_network::~dht_network() = default;
 
 void print_routing_table(std::vector<lt::dht_routing_bucket> const& rt)
 {
diff --git a/src/bdecode.cpp b/src/bdecode.cpp
index 145a663c9..f8a65bb42 100644
--- a/src/bdecode.cpp
+++ b/src/bdecode.cpp
@@ -102,7 +102,7 @@ namespace libtorrent
 
 	struct stack_frame
 	{
-		stack_frame(int const t): token(t), state(0) {}
+		explicit stack_frame(int const t): token(t), state(0) {}
 		// this is an index into m_tokens
 		std::uint32_t token:31;
 		// this is used for dictionaries to indicate whether we're
@@ -752,7 +752,7 @@ namespace libtorrent
 			switch (t)
 			{
 				case 'd':
-					stack[sp++] = int(ret.m_tokens.size());
+					stack[sp++] = stack_frame(int(ret.m_tokens.size()));
 					// we push it into the stack so that we know where to fill
 					// in the next_node field once we pop this node off the stack.
 					// i.e. get to the node following the dictionary in the buffer
@@ -761,7 +761,7 @@ namespace libtorrent
 					++start;
 					break;
 				case 'l':
-					stack[sp++] = int(ret.m_tokens.size());
+					stack[sp++] = stack_frame(int(ret.m_tokens.size()));
 					// we push it into the stack so that we know where to fill
 					// in the next_node field once we pop this node off the stack.
 					// i.e. get to the node following the list in the buffer
diff --git a/src/http_connection.cpp b/src/http_connection.cpp
index aa5bf2312..a8cc8df57 100644
--- a/src/http_connection.cpp
+++ b/src/http_connection.cpp
@@ -328,7 +328,7 @@ void http_connection::start(std::string const& hostname, int port
 #ifdef TORRENT_USE_OPENSSL
 		if (m_ssl)
 		{
-			if (m_ssl_ctx == 0)
+			if (m_ssl_ctx == nullptr)
 			{
 				m_ssl_ctx = new (std::nothrow) ssl::context(
 					m_timer.get_io_service(), ssl::context::sslv23_client);
diff --git a/src/kademlia/dht_storage.cpp b/src/kademlia/dht_storage.cpp
index 5e78dcf84..8b9fabe40 100644
--- a/src/kademlia/dht_storage.cpp
+++ b/src/kademlia/dht_storage.cpp
@@ -89,7 +89,7 @@ namespace
 	struct count_peers
 	{
 		int* count;
-		count_peers(int* c): count(c) {}
+		explicit count_peers(int* c): count(c) {}
 		void operator()(std::pair<libtorrent::sha1_hash
 			, torrent_entry> const& t)
 		{
@@ -147,7 +147,7 @@ namespace
 	// less important to keep
 	struct immutable_item_comparator
 	{
-		immutable_item_comparator(std::vector<node_id> const& node_ids) : m_node_ids(node_ids) {}
+		explicit immutable_item_comparator(std::vector<node_id> const& node_ids) : m_node_ids(node_ids) {}
 		immutable_item_comparator(immutable_item_comparator const&) = default;
 
 		bool operator() (std::pair<node_id, dht_immutable_item> const& lhs
@@ -193,7 +193,7 @@ namespace
 
 	public:
 
-		dht_default_storage(dht_settings const& settings)
+		explicit dht_default_storage(dht_settings const& settings)
 			: m_settings(settings)
 		{
 			m_counters.reset();
diff --git a/src/kademlia/dht_tracker.cpp b/src/kademlia/dht_tracker.cpp
index 1f6d8d8f2..fa2be6a4e 100644
--- a/src/kademlia/dht_tracker.cpp
+++ b/src/kademlia/dht_tracker.cpp
@@ -353,7 +353,7 @@ namespace libtorrent { namespace dht
 
 	struct get_immutable_item_ctx
 	{
-		get_immutable_item_ctx(int traversals)
+		explicit get_immutable_item_ctx(int traversals)
 			: active_traversals(traversals)
 			, item_posted(false)
 		{}
@@ -379,7 +379,7 @@ namespace libtorrent { namespace dht
 
 	struct get_mutable_item_ctx
 	{
-		get_mutable_item_ctx(int traversals) : active_traversals(traversals) {}
+		explicit get_mutable_item_ctx(int traversals) : active_traversals(traversals) {}
 		int active_traversals;
 		item it;
 	};
@@ -404,7 +404,7 @@ namespace libtorrent { namespace dht
 
 	struct put_item_ctx
 	{
-		put_item_ctx(int traversals)
+		explicit put_item_ctx(int traversals)
 			: active_traversals(traversals)
 			, response_count(0)
 		{}
diff --git a/src/lt_trackers.cpp b/src/lt_trackers.cpp
index 250e79612..709490d66 100644
--- a/src/lt_trackers.cpp
+++ b/src/lt_trackers.cpp
@@ -73,7 +73,7 @@ namespace libtorrent { namespace
 
 	struct lt_tracker_plugin : torrent_plugin
 	{
-		lt_tracker_plugin(torrent& t)
+		explicit lt_tracker_plugin(torrent& t)
 			: m_torrent(t)
 			, m_updates(0)
 			, m_2_minutes(110)
diff --git a/src/metadata_transfer.cpp b/src/metadata_transfer.cpp
index 2e5b914dc..2d25ec061 100644
--- a/src/metadata_transfer.cpp
+++ b/src/metadata_transfer.cpp
@@ -99,7 +99,7 @@ namespace libtorrent { namespace
 	struct metadata_plugin final
 		: torrent_plugin
 	{
-		metadata_plugin(torrent& t)
+		explicit metadata_plugin(torrent& t)
 			: m_torrent(t)
 			, m_metadata_progress(0)
 			, m_metadata_size(0)
diff --git a/src/peer_connection.cpp b/src/peer_connection.cpp
index e6ed20d4a..4f14cd3b6 100644
--- a/src/peer_connection.cpp
+++ b/src/peer_connection.cpp
@@ -2568,7 +2568,7 @@ namespace libtorrent
 #if TORRENT_USE_INVARIANT_CHECKS
 	struct check_postcondition
 	{
-		check_postcondition(boost::shared_ptr<torrent> const& t_
+		explicit check_postcondition(boost::shared_ptr<torrent> const& t_
 			, bool init_check = true): t(t_) { if (init_check) check(); }
 
 		~check_postcondition() { check(); }
diff --git a/src/peer_list.cpp b/src/peer_list.cpp
index 64a2f30a9..0db7c9918 100644
--- a/src/peer_list.cpp
+++ b/src/peer_list.cpp
@@ -71,7 +71,7 @@ namespace
 
 	struct match_peer_endpoint
 	{
-		match_peer_endpoint(tcp::endpoint const& ep)
+		explicit match_peer_endpoint(tcp::endpoint const& ep)
 			: m_ep(ep)
 		{}
 
@@ -87,7 +87,7 @@ namespace
 #if TORRENT_USE_INVARIANT_CHECKS
 	struct match_peer_connection
 	{
-		match_peer_connection(peer_connection_interface const& c) : m_conn(c) {}
+		explicit match_peer_connection(peer_connection_interface const& c) : m_conn(c) {}
 
 		bool operator()(torrent_peer const* p) const
 		{
@@ -102,7 +102,7 @@ namespace
 #if TORRENT_USE_ASSERTS
 	struct match_peer_connection_or_endpoint
 	{
-		match_peer_connection_or_endpoint(peer_connection_interface const& c) : m_conn(c) {}
+		explicit match_peer_connection_or_endpoint(peer_connection_interface const& c) : m_conn(c) {}
 
 		bool operator()(torrent_peer const* p) const
 		{
diff --git a/src/session.cpp b/src/session.cpp
index a3c7e4a18..cd3734b3d 100644
--- a/src/session.cpp
+++ b/src/session.cpp
@@ -403,7 +403,7 @@ namespace libtorrent
 		, std::shared_ptr<std::thread> t
 		, boost::shared_ptr<aux::session_impl> impl)
 		: m_io_service(std::move(ios))
-		, m_thread(t)
+		, m_thread(std::move(t))
 		, m_impl(impl)
 	{}
 	session_proxy::session_proxy(session_proxy const&) = default;
diff --git a/src/session_impl.cpp b/src/session_impl.cpp
index b58dc0064..6d072c3a4 100644
--- a/src/session_impl.cpp
+++ b/src/session_impl.cpp
@@ -776,7 +776,7 @@ namespace aux {
 
 	struct session_plugin_wrapper : plugin
 	{
-		session_plugin_wrapper(ext_function_t const& f) : m_f(f) {}
+		explicit session_plugin_wrapper(ext_function_t const& f) : m_f(f) {}
 
 		boost::shared_ptr<torrent_plugin> new_torrent(torrent_handle const& t, void* user) override
 		{ return m_f(t, user); }
@@ -3736,7 +3736,7 @@ namespace aux {
 
 		struct opt_unchoke_candidate
 		{
-			opt_unchoke_candidate(boost::shared_ptr<peer_connection> const* tp)
+			explicit opt_unchoke_candidate(boost::shared_ptr<peer_connection> const* tp)
 				: peer(tp)
 			{}
 
@@ -3752,7 +3752,7 @@ namespace aux {
 		struct last_optimistic_unchoke_cmp
 		{
 #ifndef TORRENT_DISABLE_EXTENSIONS
-			last_optimistic_unchoke_cmp(std::vector<boost::shared_ptr<plugin>>& ps)
+			explicit last_optimistic_unchoke_cmp(std::vector<boost::shared_ptr<plugin>>& ps)
 				: plugins(ps)
 			{}
 
diff --git a/src/smart_ban.cpp b/src/smart_ban.cpp
index 2e3a8ae79..0ae992217 100644
--- a/src/smart_ban.cpp
+++ b/src/smart_ban.cpp
@@ -76,7 +76,7 @@ namespace
 		: torrent_plugin
 		, boost::enable_shared_from_this<smart_ban_plugin>
 	{
-		smart_ban_plugin(torrent& t)
+		explicit smart_ban_plugin(torrent& t)
 			: m_torrent(t)
 			, m_salt(random())
 		{}
diff --git a/src/socket_type.cpp b/src/socket_type.cpp
index ee0078f1f..ca556961c 100644
--- a/src/socket_type.cpp
+++ b/src/socket_type.cpp
@@ -100,8 +100,8 @@ namespace libtorrent
 		ctx = SSL_get_SSL_CTX(ssl); \
 		break;
 
-		SSL* ssl = 0;
-		SSL_CTX* ctx = 0;
+		SSL* ssl = nullptr;
+		SSL_CTX* ctx = nullptr;
 
 		switch(s.type())
 		{
@@ -115,8 +115,8 @@ namespace libtorrent
 #if OPENSSL_VERSION_NUMBER >= 0x90812f
 		if (ctx)
 		{
-			aux::openssl_set_tlsext_servername_callback(ctx, 0);
-			aux::openssl_set_tlsext_servername_arg(ctx, 0);
+			aux::openssl_set_tlsext_servername_callback(ctx, nullptr);
+			aux::openssl_set_tlsext_servername_arg(ctx, nullptr);
 		}
 #endif // OPENSSL_VERSION_NUMBER
 
diff --git a/src/torrent.cpp b/src/torrent.cpp
index fdd9dd9af..590e9ff16 100644
--- a/src/torrent.cpp
+++ b/src/torrent.cpp
@@ -1488,7 +1488,7 @@ namespace libtorrent
 
 		// Go through the alternate names in the certificate looking for matching DNS entries
 		GENERAL_NAMES* gens = static_cast<GENERAL_NAMES*>(
-			X509_get_ext_d2i(cert, NID_subject_alt_name, 0, 0));
+			X509_get_ext_d2i(cert, NID_subject_alt_name, nullptr, nullptr));
 
 #ifndef TORRENT_DISABLE_LOGGING
 		std::string names;
@@ -1525,7 +1525,7 @@ namespace libtorrent
 		// use the "most specific" common name, which is the last one in the list.
 		X509_NAME* name = X509_get_subject_name(cert);
 		int i = -1;
-		ASN1_STRING* common_name = 0;
+		ASN1_STRING* common_name = nullptr;
 		while ((i = X509_NAME_get_index_by_NID(name, NID_commonName, i)) >= 0)
 		{
 			X509_NAME_ENTRY* name_entry = X509_NAME_get_entry(name, i);
@@ -1637,7 +1637,7 @@ namespace libtorrent
 
 		// parse the certificate into OpenSSL's internal
 		// representation
-		X509* certificate = PEM_read_bio_X509_AUX(bp, 0, 0, 0);
+		X509* certificate = PEM_read_bio_X509_AUX(bp, nullptr, nullptr, nullptr);
 
 		BIO_free(bp);
 
@@ -7100,7 +7100,7 @@ namespace libtorrent
 			ssl_conn = s->get<ssl_stream<t> >()->native_handle(); \
 			break;
 
-			SSL* ssl_conn = 0;
+			SSL* ssl_conn = nullptr;
 
 			switch (s->type())
 			{
@@ -7112,7 +7112,7 @@ namespace libtorrent
 
 #undef SSL
 
-			if (ssl_conn == 0)
+			if (ssl_conn == nullptr)
 			{
 				// don't allow non SSL peers on SSL torrents
 				p->disconnect(errors::requires_ssl_connection, op_bittorrent);
diff --git a/src/torrent_info.cpp b/src/torrent_info.cpp
index 073d75831..e60a1786c 100644
--- a/src/torrent_info.cpp
+++ b/src/torrent_info.cpp
@@ -1539,7 +1539,7 @@ namespace libtorrent
 	{
 		struct filter_web_seed_type
 		{
-			filter_web_seed_type(web_seed_entry::type_t t_) : t(t_) {}
+			explicit filter_web_seed_type(web_seed_entry::type_t t_) : t(t_) {}
 			void operator() (web_seed_entry const& w)
 			{ if (w.type == t) urls.push_back(w.url); }
 			std::vector<std::string> urls;
diff --git a/src/udp_socket.cpp b/src/udp_socket.cpp
index 80dc8afd8..db9783e45 100644
--- a/src/udp_socket.cpp
+++ b/src/udp_socket.cpp
@@ -74,7 +74,7 @@ using namespace std::placeholders;
 //    the common case cheaper by not allocating this space unconditionally
 struct socks5 : boost::enable_shared_from_this<socks5>
 {
-	socks5(io_service& ios)
+	explicit socks5(io_service& ios)
 		: m_socks5_sock(ios)
 		, m_resolver(ios)
 		, m_timer(ios)
diff --git a/src/ut_metadata.cpp b/src/ut_metadata.cpp
index 68b8d5d00..3a23fc11e 100644
--- a/src/ut_metadata.cpp
+++ b/src/ut_metadata.cpp
@@ -95,7 +95,7 @@ namespace libtorrent { namespace
 	struct ut_metadata_plugin final
 		: torrent_plugin
 	{
-		ut_metadata_plugin(torrent& t)
+		explicit ut_metadata_plugin(torrent& t)
 			: m_torrent(t)
 //			, m_metadata_progress(0)
 			, m_metadata_size(0)
diff --git a/src/ut_pex.cpp b/src/ut_pex.cpp
index 82a515d71..242e12eab 100644
--- a/src/ut_pex.cpp
+++ b/src/ut_pex.cpp
@@ -88,7 +88,7 @@ namespace libtorrent { namespace
 		// to evenly spread it out across all torrents
 		// the more torrents we have, the longer we can
 		// delay the rebuilding
-		ut_pex_plugin(torrent& t)
+		explicit ut_pex_plugin(torrent& t)
 			: m_torrent(t)
 			, m_last_msg(min_time())
 			, m_peers_in_message(0) {}
diff --git a/src/utp_stream.cpp b/src/utp_stream.cpp
index 30d78c928..59e744206 100644
--- a/src/utp_stream.cpp
+++ b/src/utp_stream.cpp
@@ -1723,7 +1723,7 @@ void utp_socket_impl::remove_sack_header(packet* p)
 
 struct holder
 {
-	holder(char* buf = nullptr): m_buf(buf) {}
+	explicit holder(char* buf = nullptr): m_buf(buf) {}
 	~holder() { free(m_buf); }
 
 	void reset(char* buf)
diff --git a/test/test_alert_manager.cpp b/test/test_alert_manager.cpp
index 9e774d22b..0c9f8b023 100644
--- a/test/test_alert_manager.cpp
+++ b/test/test_alert_manager.cpp
@@ -156,7 +156,7 @@ int plugin_alerts[3] = { 0, 0, 0 };
 
 struct test_plugin : libtorrent::plugin
 {
-	test_plugin(int index) : m_index(index) {}
+	explicit test_plugin(int index) : m_index(index) {}
 	void on_alert(alert const* a) override
 	{
 		++plugin_alerts[m_index];
diff --git a/test/test_heterogeneous_queue.cpp b/test/test_heterogeneous_queue.cpp
index 5c376e65e..cb1d14e4c 100644
--- a/test/test_heterogeneous_queue.cpp
+++ b/test/test_heterogeneous_queue.cpp
@@ -69,7 +69,7 @@ struct D
 
 struct E
 {
-	E(char const* msg) : string_member(msg) {}
+	explicit E(char const* msg) : string_member(msg) {}
 	std::string string_member;
 };
 
@@ -77,7 +77,7 @@ int D::instances = 0;
 
 struct F
 {
-	F(int f_)
+	explicit F(int f_)
 		: self(this)
 		, f(f_)
 		, constructed(true)
diff --git a/test/test_linked_list.cpp b/test/test_linked_list.cpp
index 5ffb89d32..0e182da06 100644
--- a/test/test_linked_list.cpp
+++ b/test/test_linked_list.cpp
@@ -37,7 +37,7 @@ using namespace libtorrent;
 
 struct test_node : list_node<test_node>
 {
-	test_node(int v) : val(v) {}
+	explicit test_node(int v) : val(v) {}
 	int val;
 };
 
diff --git a/test/test_peer_list.cpp b/test/test_peer_list.cpp
index 5b9bafdd6..5e2fe1a0e 100644
--- a/test/test_peer_list.cpp
+++ b/test/test_peer_list.cpp
@@ -113,7 +113,7 @@ struct mock_peer_connection
 
 struct mock_torrent
 {
-	mock_torrent(torrent_state* st) : m_p(nullptr), m_state(st) {}
+	explicit mock_torrent(torrent_state* st) : m_p(nullptr), m_state(st) {}
 	virtual ~mock_torrent() = default;
 
 	bool connect_to_peer(torrent_peer* peerinfo, bool ignore_limit = false)
diff --git a/test/test_ssl.cpp b/test/test_ssl.cpp
index b65a36071..2ca860536 100644
--- a/test/test_ssl.cpp
+++ b/test/test_ssl.cpp
@@ -196,7 +196,7 @@ void test_ssl(int test_idx, bool use_utp)
 	ssl_peer_disconnects = 0;
 	peer_errors = 0;
 
-	std::tie(tor1, tor2, ignore) = setup_transfer(&ses1, &ses2, 0
+	std::tie(tor1, tor2, ignore) = setup_transfer(&ses1, &ses2, nullptr
 		, true, false, false, "_ssl", 16 * 1024, &t, false, &addp, true);
 
 	if (test.seed_has_cert)
diff --git a/test/test_storage.cpp b/test/test_storage.cpp
index eaf6c2966..5d1e461ef 100644
--- a/test/test_storage.cpp
+++ b/test/test_storage.cpp
@@ -1022,7 +1022,7 @@ file_storage make_fs()
 
 struct test_fileop : fileop
 {
-	test_fileop(int stripe_size) : m_stripe_size(stripe_size) {}
+	explicit test_fileop(int stripe_size) : m_stripe_size(stripe_size) {}
 
 	int file_op(int const file_index, std::int64_t const file_offset, int const size
 		, file::iovec_t const* bufs, storage_error& ec) override
@@ -1061,7 +1061,7 @@ struct test_fileop : fileop
 struct test_read_fileop : fileop
 {
 	// EOF after size bytes read
-	test_read_fileop(int size) : m_size(size), m_counter(0) {}
+	explicit test_read_fileop(int size) : m_size(size), m_counter(0) {}
 
 	int file_op(int const file_index, std::int64_t const file_offset, int const size
 		, file::iovec_t const* bufs, storage_error& ec) override
@@ -1091,7 +1091,7 @@ struct test_read_fileop : fileop
 struct test_error_fileop : fileop
 {
 	// EOF after size bytes read
-	test_error_fileop(int error_file)
+	explicit test_error_fileop(int error_file)
 		: m_error_file(error_file) {}
 
 	int file_op(int const file_index, std::int64_t const file_offset, int const size
diff --git a/test/test_tailqueue.cpp b/test/test_tailqueue.cpp
index b838a1943..b55fd3290 100644
--- a/test/test_tailqueue.cpp
+++ b/test/test_tailqueue.cpp
@@ -37,7 +37,7 @@ using namespace libtorrent;
 
 struct test_node : tailqueue_node<test_node>
 {
-	test_node(char n) : name(n) {}
+	explicit test_node(char n) : name(n) {}
 	char name;
 };
 
diff --git a/test/test_torrent.cpp b/test/test_torrent.cpp
index 284a49b9d..59b083dfb 100644
--- a/test/test_torrent.cpp
+++ b/test/test_torrent.cpp
@@ -312,7 +312,7 @@ struct test_plugin : libtorrent::torrent_plugin {};
 
 struct plugin_creator
 {
-	plugin_creator(int& c) : m_called(c) {}
+	explicit plugin_creator(int& c) : m_called(c) {}
 
 	boost::shared_ptr<libtorrent::torrent_plugin>
 	operator()(torrent_handle const&, void*)
diff --git a/test/test_transfer.cpp b/test/test_transfer.cpp
index 21e3cdd3b..4430b7538 100644
--- a/test/test_transfer.cpp
+++ b/test/test_transfer.cpp
@@ -71,7 +71,7 @@ bool on_alert(alert const* a)
 // simulate a full disk
 struct test_storage : default_storage
 {
-	test_storage(storage_params const& params)
+	explicit test_storage(storage_params const& params)
 		: default_storage(params)
 		, m_written(0)
 		, m_limit(16 * 1024 * 2)