diff --git a/include/libtorrent/alert_types.hpp b/include/libtorrent/alert_types.hpp
index 2e8fb8334..9332caf93 100644
--- a/include/libtorrent/alert_types.hpp
+++ b/include/libtorrent/alert_types.hpp
@@ -2687,7 +2687,7 @@ namespace libtorrent {
 #undef TORRENT_DEFINE_ALERT
 #undef TORRENT_DEFINE_ALERT_PRIO
 
-	enum { num_alert_types = 95 }; // this enum represents "max_alert_index" + 1
+	constexpr int num_alert_types = 95; // this constant represents "max_alert_index" + 1
 }
 
 #endif
diff --git a/include/libtorrent/aux_/session_impl.hpp b/include/libtorrent/aux_/session_impl.hpp
index a88320a42..d6f07b7cc 100644
--- a/include/libtorrent/aux_/session_impl.hpp
+++ b/include/libtorrent/aux_/session_impl.hpp
@@ -240,7 +240,8 @@ namespace aux {
 			, std::enable_shared_from_this<session_impl>
 		{
 			// the size of each allocation that is chained in the send buffer
-			enum { send_buffer_size_impl = 128 };
+			static constexpr int send_buffer_size_impl = 128;
+
 			// plugin feature-index key map
 			enum
 			{
diff --git a/include/libtorrent/block_cache.hpp b/include/libtorrent/block_cache.hpp
index 35ce78d4d..77e9c4e49 100644
--- a/include/libtorrent/block_cache.hpp
+++ b/include/libtorrent/block_cache.hpp
@@ -129,7 +129,7 @@ namespace aux {
 
 		char* buf;
 
-		enum { max_refcount = (1 << 29) - 1 };
+		static constexpr int max_refcount = (1 << 29) - 1;
 
 		// the number of references to this buffer. These references
 		// might be in outstanding asynchronous requests or in peer
diff --git a/include/libtorrent/kademlia/dos_blocker.hpp b/include/libtorrent/kademlia/dos_blocker.hpp
index 84a35ea21..3a15e1e17 100644
--- a/include/libtorrent/kademlia/dos_blocker.hpp
+++ b/include/libtorrent/kademlia/dos_blocker.hpp
@@ -76,7 +76,7 @@ namespace libtorrent { namespace dht {
 			int count;
 		};
 
-		enum { num_ban_nodes = 20 };
+		static constexpr int num_ban_nodes = 20;
 
 		// the max number of packets we can receive per second from a node before
 		// we block it.
diff --git a/include/libtorrent/peer_connection.hpp b/include/libtorrent/peer_connection.hpp
index d0f65d15f..7595ae407 100644
--- a/include/libtorrent/peer_connection.hpp
+++ b/include/libtorrent/peer_connection.hpp
@@ -99,7 +99,7 @@ namespace aux {
 
 		piece_block block;
 
-		enum { not_in_buffer = 0x1fffffff };
+		static constexpr std::uint32_t not_in_buffer = 0x1fffffff;
 
 		// the number of bytes into the send buffer this request is. Every time
 		// some portion of the send buffer is transmitted, this offset is
diff --git a/include/libtorrent/piece_picker.hpp b/include/libtorrent/piece_picker.hpp
index 52c59be59..2bfd17bf8 100644
--- a/include/libtorrent/piece_picker.hpp
+++ b/include/libtorrent/piece_picker.hpp
@@ -577,15 +577,13 @@ namespace libtorrent {
 			// index is set to this to indicate that we have the
 			// piece. There is no entry for the piece in the
 			// buckets if this is the case.
-			constexpr static prio_index_t we_have_index{-1};
+			static constexpr prio_index_t we_have_index{-1};
 
-			enum : std::uint32_t
-			{
-				// the priority value that means the piece is filtered
-				filter_priority = 0,
-				// the max number the peer count can hold
-				max_peer_count = 0xffff
-			};
+			// the priority value that means the piece is filtered
+			static constexpr std::uint32_t filter_priority = 0;
+
+			// the max number the peer count can hold
+			static constexpr std::uint32_t max_peer_count = 0xffff;
 
 			bool have() const { return index == we_have_index; }
 			void set_have() { index = we_have_index; TORRENT_ASSERT(have()); }
diff --git a/include/libtorrent/sha1_hash.hpp b/include/libtorrent/sha1_hash.hpp
index c9b454668..88610615f 100644
--- a/include/libtorrent/sha1_hash.hpp
+++ b/include/libtorrent/sha1_hash.hpp
@@ -67,7 +67,7 @@ namespace aux {
 	class digest32
 	{
 		static_assert(N % 32 == 0, "N must be a multiple of 32");
-		enum { number_size = N / 32 };
+		static constexpr int number_size = N / 32;
 	public:
 
 		// the size of the hash in bytes
@@ -143,14 +143,14 @@ namespace aux {
 		// shift left ``n`` bits.
 		digest32& operator<<=(int n)
 		{
-			aux::bits_shift_left({m_number, number_size}, n);
+			aux::bits_shift_left({m_number, std::size_t(number_size)}, n);
 			return *this;
 		}
 
 		// shift right ``n`` bits.
 		digest32& operator>>=(int n)
 		{
-			aux::bits_shift_right({m_number, number_size}, n);
+			aux::bits_shift_right({m_number, std::size_t(number_size)}, n);
 			return *this;
 		}
 
@@ -177,7 +177,7 @@ namespace aux {
 
 		int count_leading_zeroes() const
 		{
-			return aux::count_leading_zeros({m_number, number_size});
+			return aux::count_leading_zeros({m_number, std::size_t(number_size)});
 		}
 
 		// returns a bit-wise negated copy of the digest
diff --git a/include/libtorrent/socket_type.hpp b/include/libtorrent/socket_type.hpp
index 6673e2222..ce1dc64b4 100644
--- a/include/libtorrent/socket_type.hpp
+++ b/include/libtorrent/socket_type.hpp
@@ -133,46 +133,46 @@ namespace libtorrent {
 
 	template <class S>
 	struct socket_type_int_impl
-	{ enum { value = 0 }; };
+	{ static constexpr int value = 0; };
 
 	template <>
 	struct socket_type_int_impl<tcp::socket>
-	{ enum { value = 1 }; };
+	{ static constexpr int value = 1; };
 
 	template <>
 	struct socket_type_int_impl<socks5_stream>
-	{ enum { value = 2 }; };
+	{ static constexpr int value = 2; };
 
 	template <>
 	struct socket_type_int_impl<http_stream>
-	{ enum { value = 3 }; };
+	{ static constexpr int value = 3; };
 
 	template <>
 	struct socket_type_int_impl<utp_stream>
-	{ enum { value = 4 }; };
+	{ static constexpr int value = 4; };
 
 #if TORRENT_USE_I2P
 	template <>
 	struct socket_type_int_impl<i2p_stream>
-	{ enum { value = 5 }; };
+	{ static constexpr int value = 5; };
 #endif
 
 #ifdef TORRENT_USE_OPENSSL
 	template <>
 	struct socket_type_int_impl<ssl_stream<tcp::socket>>
-	{ enum { value = 6 }; };
+	{ static constexpr int value = 6; };
 
 	template <>
 	struct socket_type_int_impl<ssl_stream<socks5_stream>>
-	{ enum { value = 7 }; };
+	{ static constexpr int value = 7; };
 
 	template <>
 	struct socket_type_int_impl<ssl_stream<http_stream>>
-	{ enum { value = 8 }; };
+	{ static constexpr int value = 8; };
 
 	template <>
 	struct socket_type_int_impl<ssl_stream<utp_stream>>
-	{ enum { value = 9 }; };
+	{ static constexpr int value = 9; };
 #endif
 
 	struct TORRENT_EXTRA_EXPORT socket_type
diff --git a/include/libtorrent/timestamp_history.hpp b/include/libtorrent/timestamp_history.hpp
index 59049188f..ff784b1aa 100644
--- a/include/libtorrent/timestamp_history.hpp
+++ b/include/libtorrent/timestamp_history.hpp
@@ -44,7 +44,7 @@ namespace libtorrent {
 // seen in the last 20 minutes
 struct TORRENT_EXTRA_EXPORT timestamp_history
 {
-	enum { history_size = 20 };
+	static constexpr int history_size = 20;
 
 	timestamp_history() : m_base(0), m_index(0), m_num_samples(not_initialized) {}
 	bool initialized() const { return m_num_samples != not_initialized; }
@@ -68,7 +68,7 @@ private:
 	// in the circular buffer
 	std::uint16_t m_index;
 
-	enum { not_initialized = 0xffff };
+	static constexpr std::uint16_t not_initialized = 0xffff;
 
 	// this is the number of samples since the
 	// last time we stepped one minute. If we
diff --git a/include/libtorrent/torrent.hpp b/include/libtorrent/torrent.hpp
index 4221901cd..f39da3ccf 100644
--- a/include/libtorrent/torrent.hpp
+++ b/include/libtorrent/torrent.hpp
@@ -1135,7 +1135,7 @@ namespace libtorrent {
 		}
 		void add_suggest_piece(piece_index_t index);
 
-		enum { no_gauge_state = 0xf };
+		static constexpr int no_gauge_state = 0xf;
 
 	private:
 
diff --git a/include/libtorrent/upnp.hpp b/include/libtorrent/upnp.hpp
index cc72b7688..5bc2f5e8d 100644
--- a/include/libtorrent/upnp.hpp
+++ b/include/libtorrent/upnp.hpp
@@ -202,12 +202,6 @@ private:
 	static address_v4 upnp_multicast_address;
 	static udp::endpoint upnp_multicast_endpoint;
 
-	// there are routers that's don't support timed
-	// port maps, without returning error 725. It seems
-	// safer to always assume that we have to ask for
-	// permanent leases
-	enum { default_lease_time = 0 };
-
 	void resend_request(error_code const& e);
 	void on_reply(udp::endpoint const& from, char* buffer
 		, std::size_t bytes_transferred);
@@ -294,7 +288,11 @@ private:
 		std::string path;
 		address external_ip;
 
-		int lease_duration = default_lease_time;
+		// there are routers that's don't support timed
+		// port maps, without returning error 725. It seems
+		// safer to always assume that we have to ask for
+		// permanent leases
+		int lease_duration = 0;
 
 		// true if the device supports specifying a
 		// specific external port, false if it doesn't
diff --git a/src/enum_net.cpp b/src/enum_net.cpp
index 4ca5b121b..eb64f9ce4 100644
--- a/src/enum_net.cpp
+++ b/src/enum_net.cpp
@@ -100,7 +100,8 @@ const unsigned long siocgifmtu = SIOCGIFMTU;
 #define IF_NAMESIZE IFNAMSIZ
 #endif
 
-namespace libtorrent {namespace {
+namespace libtorrent {
+namespace {
 
 
 #if !defined TORRENT_BUILD_SIMULATOR
@@ -201,7 +202,7 @@ namespace libtorrent {namespace {
 		return msg_len;
 	}
 
-	enum { NL_BUFSIZE = 8192 };
+	constexpr int NL_BUFSIZE = 8192;
 
 	int nl_dump_request(int sock, std::uint16_t type, std::uint32_t seq, char family, span<char> msg, std::size_t msg_len)
 	{
@@ -495,9 +496,7 @@ int _System __libsocket_sysctl(int* mib, u_int namelen, void *oldp, size_t *oldl
 	}
 #endif
 
-}} // <anonymous>
-
-namespace libtorrent {
+} // <anonymous>
 
 	// return (a1 & mask) == (a2 & mask)
 	bool match_addr_mask(address const& a1, address const& a2, address const& mask)
diff --git a/src/kademlia/dht_storage.cpp b/src/kademlia/dht_storage.cpp
index a04598d08..700590360 100644
--- a/src/kademlia/dht_storage.cpp
+++ b/src/kademlia/dht_storage.cpp
@@ -78,7 +78,7 @@ namespace {
 	};
 
 	// TODO: 2 make this configurable in dht_settings
-	enum { announce_interval = 30 };
+	constexpr time_duration announce_interval = minutes(30);
 
 	struct dht_immutable_item
 	{
@@ -552,7 +552,7 @@ namespace {
 			auto new_end = std::remove_if(peers.begin(), peers.end()
 				, [=](peer_entry const& e)
 			{
-				return e.added + minutes(int(announce_interval * 3 / 2)) < now;
+				return e.added + announce_interval * 3 / 2 < now;
 			});
 
 			m_counters.peers -= std::int32_t(std::distance(new_end, peers.end()));
diff --git a/src/torrent.cpp b/src/torrent.cpp
index 1d78b82f8..a72f4577b 100644
--- a/src/torrent.cpp
+++ b/src/torrent.cpp
@@ -210,7 +210,7 @@ namespace libtorrent {
 		, m_ssl_torrent(false)
 		, m_deleted(false)
 		, m_auto_managed(p.flags & torrent_flags::auto_managed)
-		, m_current_gauge_state(no_gauge_state)
+		, m_current_gauge_state(static_cast<std::uint32_t>(no_gauge_state))
 		, m_moving_storage(false)
 		, m_inactive(false)
 		, m_downloaded(0xffffff)
@@ -534,7 +534,9 @@ namespace libtorrent {
 		if (new_gauge_state != no_gauge_state)
 			inc_stats_counter(new_gauge_state + counters::num_checking_torrents, 1);
 
-		m_current_gauge_state = aux::numeric_cast<std::uint8_t>(new_gauge_state);
+		TORRENT_ASSERT(new_gauge_state >= 0);
+		TORRENT_ASSERT(new_gauge_state <= no_gauge_state);
+		m_current_gauge_state = static_cast<std::uint32_t>(new_gauge_state);
 	}
 
 	void torrent::leave_seed_mode(bool skip_checking)
@@ -9345,7 +9347,7 @@ namespace libtorrent {
 	{
 		// this is a silly optimization
 		// to avoid copying of strings
-		enum { num_strings = 200 };
+		int const num_strings = 200;
 		static char buf[num_strings][20];
 		static int round_robin = 0;
 		char* ret = buf[round_robin];
diff --git a/src/upnp.cpp b/src/upnp.cpp
index 558f81060..27cd45176 100644
--- a/src/upnp.cpp
+++ b/src/upnp.cpp
@@ -1377,7 +1377,7 @@ void upnp::on_upnp_map_response(error_code const& e
 
 	if (s.error_code == 725)
 	{
-		// only permanent leases supported
+		// The gateway only supports permanent leases
 		d.lease_duration = 0;
 		m.act = portmap_action::add;
 		++m.failcount;