diff --git a/.github/workflows/android.yml b/.github/workflows/android.yml
index a5133a94..2e2f9138 100644
--- a/.github/workflows/android.yml
+++ b/.github/workflows/android.yml
@@ -18,7 +18,7 @@ jobs:
     - name: Set up Docker Buildx
       uses: docker/setup-buildx-action@v3
     - name: Build
-      uses: docker/build-push-action@v5
+      uses: docker/build-push-action@v6
       with:
         file: Dockerfile.android
         context: .
diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 95657a78..3f538aad 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -28,12 +28,12 @@ jobs:
   build:
     strategy:
       matrix:
-        os: [ubuntu-22.04, macos-11]
+        os: [ubuntu-22.04, macos-14]
         compiler: [gcc, clang]
         crypto: [openssl, gnutls]
         bittorrent: [with-bt, without-bt]
         exclude:
-        - os: macos-11
+        - os: macos-14
           crypto: gnutls
         - crypto: openssl
           bittorrent: without-bt
diff --git a/configure.ac b/configure.ac
index 88778a33..98439946 100644
--- a/configure.ac
+++ b/configure.ac
@@ -503,18 +503,10 @@ fi
 
 have_libcares=no
 if test "x$with_libcares" = "xyes"; then
-  PKG_CHECK_MODULES([LIBCARES], [libcares >= 1.7.0], [have_libcares=yes],
+  PKG_CHECK_MODULES([LIBCARES], [libcares >= 1.16.0], [have_libcares=yes],
                     [have_libcares=no])
   if test "x$have_libcares" = "xyes"; then
     AC_DEFINE([HAVE_LIBCARES], [1], [Define to 1 if you have libcares.])
-    save_LIBS=$LIBS
-    save_CPPFLAGS=$CPPFLAGS
-    LIBS="$LIBCARES_LIBS $LIBS"
-    CPPFLAGS="$LIBCARES_CFLAGS $CPPFLAGS"
-    AC_CHECK_TYPES([ares_addr_node], [], [], [[#include <ares.h>]])
-    AC_CHECK_FUNCS([ares_set_servers])
-    LIBS=$save_LIBS
-    CPPFLAGS=$save_CPPFLAGS
 
     # -DCARES_STATICLIB is appended by pkg-config file libcares.pc
   else
diff --git a/src/AsyncNameResolver.cc b/src/AsyncNameResolver.cc
index b041d6f9..09e85229 100644
--- a/src/AsyncNameResolver.cc
+++ b/src/AsyncNameResolver.cc
@@ -40,10 +40,11 @@
 #include "LogFactory.h"
 #include "SocketCore.h"
 #include "util.h"
+#include "EventPoll.h"
 
 namespace aria2 {
 
-void callback(void* arg, int status, int timeouts, struct hostent* host)
+void callback(void* arg, int status, int timeouts, ares_addrinfo* result)
 {
   AsyncNameResolver* resolverPtr = reinterpret_cast<AsyncNameResolver*>(arg);
   if (status != ARES_SUCCESS) {
@@ -51,12 +52,15 @@ void callback(void* arg, int status, int timeouts, struct hostent* host)
     resolverPtr->status_ = AsyncNameResolver::STATUS_ERROR;
     return;
   }
-  for (char** ap = host->h_addr_list; *ap; ++ap) {
+  for (auto ap = result->nodes; ap; ap = ap->ai_next) {
     char addrstring[NI_MAXHOST];
-    if (inetNtop(host->h_addrtype, *ap, addrstring, sizeof(addrstring)) == 0) {
+    auto rv = getnameinfo(ap->ai_addr, ap->ai_addrlen, addrstring,
+                          sizeof(addrstring), nullptr, 0, NI_NUMERICHOST);
+    if (rv == 0) {
       resolverPtr->resolvedAddresses_.push_back(addrstring);
     }
   }
+  ares_freeaddrinfo(result);
   if (resolverPtr->resolvedAddresses_.empty()) {
     resolverPtr->error_ = "no address returned or address conversion failed";
     resolverPtr->status_ = AsyncNameResolver::STATUS_ERROR;
@@ -66,24 +70,63 @@ void callback(void* arg, int status, int timeouts, struct hostent* host)
   }
 }
 
-AsyncNameResolver::AsyncNameResolver(int family
-#ifdef HAVE_ARES_ADDR_NODE
-                                     ,
-                                     ares_addr_node* servers
-#endif // HAVE_ARES_ADDR_NODE
-                                     )
+namespace {
+void sock_state_cb(void* arg, ares_socket_t fd, int read, int write)
+{
+  auto resolver = static_cast<AsyncNameResolver*>(arg);
+
+  resolver->handle_sock_state(fd, read, write);
+}
+} // namespace
+
+void AsyncNameResolver::handle_sock_state(ares_socket_t fd, int read, int write)
+{
+  int events = 0;
+
+  if (read) {
+    events |= EventPoll::EVENT_READ;
+  }
+
+  if (write) {
+    events |= EventPoll::EVENT_WRITE;
+  }
+
+  auto it = std::find_if(
+      std::begin(socks_), std::end(socks_),
+      [fd](const AsyncNameResolverSocketEntry& ent) { return ent.fd == fd; });
+  if (it == std::end(socks_)) {
+    if (!events) {
+      return;
+    }
+
+    socks_.emplace_back(AsyncNameResolverSocketEntry{fd, events});
+
+    return;
+  }
+
+  if (!events) {
+    socks_.erase(it);
+    return;
+  }
+
+  (*it).events = events;
+}
+
+AsyncNameResolver::AsyncNameResolver(int family, const std::string& servers)
     : status_(STATUS_READY), family_(family)
 {
+  ares_options opts{};
+  opts.sock_state_cb = sock_state_cb;
+  opts.sock_state_cb_data = this;
+
   // TODO evaluate return value
-  ares_init(&channel_);
-#if defined(HAVE_ARES_SET_SERVERS) && defined(HAVE_ARES_ADDR_NODE)
-  if (servers) {
-    // ares_set_servers has been added since c-ares 1.7.1
-    if (ares_set_servers(channel_, servers) != ARES_SUCCESS) {
-      A2_LOG_DEBUG("ares_set_servers failed");
+  ares_init_options(&channel_, &opts, ARES_OPT_SOCK_STATE_CB);
+
+  if (!servers.empty()) {
+    if (ares_set_servers_csv(channel_, servers.c_str()) != ARES_SUCCESS) {
+      A2_LOG_DEBUG("ares_set_servers_csv failed");
     }
   }
-#endif // HAVE_ARES_SET_SERVERS && HAVE_ARES_ADDR_NODE
 }
 
 AsyncNameResolver::~AsyncNameResolver() { ares_destroy(channel_); }
@@ -92,25 +135,58 @@ void AsyncNameResolver::resolve(const std::string& name)
 {
   hostname_ = name;
   status_ = STATUS_QUERYING;
-  ares_gethostbyname(channel_, name.c_str(), family_, callback, this);
+
+  ares_addrinfo_hints hints{};
+  hints.ai_family = family_;
+
+  ares_getaddrinfo(channel_, name.c_str(), nullptr, &hints, callback, this);
 }
 
-int AsyncNameResolver::getFds(fd_set* rfdsPtr, fd_set* wfdsPtr) const
+ares_socket_t AsyncNameResolver::getFds(fd_set* rfdsPtr, fd_set* wfdsPtr) const
 {
-  return ares_fds(channel_, rfdsPtr, wfdsPtr);
+  ares_socket_t nfds = 0;
+
+  for (const auto& ent : socks_) {
+    if (ent.events & EventPoll::EVENT_READ) {
+      FD_SET(ent.fd, rfdsPtr);
+      nfds = std::max(nfds, ent.fd + 1);
+    }
+
+    if (ent.events & EventPoll::EVENT_WRITE) {
+      FD_SET(ent.fd, wfdsPtr);
+      nfds = std::max(nfds, ent.fd + 1);
+    }
+  }
+
+  return nfds;
 }
 
 void AsyncNameResolver::process(fd_set* rfdsPtr, fd_set* wfdsPtr)
 {
-  ares_process(channel_, rfdsPtr, wfdsPtr);
+  for (const auto& ent : socks_) {
+    ares_socket_t readfd = ARES_SOCKET_BAD;
+    ares_socket_t writefd = ARES_SOCKET_BAD;
+
+    if (FD_ISSET(ent.fd, rfdsPtr) && (ent.events & EventPoll::EVENT_READ)) {
+      readfd = ent.fd;
+    }
+
+    if (FD_ISSET(ent.fd, wfdsPtr) && (ent.events & EventPoll::EVENT_WRITE)) {
+      writefd = ent.fd;
+    }
+
+    if (readfd != ARES_SOCKET_BAD || writefd != ARES_SOCKET_BAD) {
+      process(readfd, writefd);
+    }
+  }
 }
 
 #ifdef HAVE_LIBCARES
 
-int AsyncNameResolver::getsock(sock_t* sockets) const
+const std::vector<AsyncNameResolverSocketEntry>&
+AsyncNameResolver::getsock() const
 {
-  return ares_getsock(channel_, reinterpret_cast<ares_socket_t*>(sockets),
-                      ARES_GETSOCK_MAXNUM);
+  return socks_;
 }
 
 void AsyncNameResolver::process(ares_socket_t readfd, ares_socket_t writefd)
@@ -125,41 +201,4 @@ bool AsyncNameResolver::operator==(const AsyncNameResolver& resolver) const
   return this == &resolver;
 }
 
-void AsyncNameResolver::reset()
-{
-  hostname_ = A2STR::NIL;
-  resolvedAddresses_.clear();
-  status_ = STATUS_READY;
-  ares_destroy(channel_);
-  // TODO evaluate return value
-  ares_init(&channel_);
-}
-
-#ifdef HAVE_ARES_ADDR_NODE
-
-ares_addr_node* parseAsyncDNSServers(const std::string& serversOpt)
-{
-  std::vector<std::string> servers;
-  util::split(std::begin(serversOpt), std::end(serversOpt),
-              std::back_inserter(servers), ',', true /* doStrip */);
-  ares_addr_node root;
-  root.next = nullptr;
-  ares_addr_node* tail = &root;
-  for (const auto& s : servers) {
-    auto node = make_unique<ares_addr_node>();
-
-    size_t len = net::getBinAddr(&node->addr, s.c_str());
-    if (len != 0) {
-      node->next = nullptr;
-      node->family = (len == 4 ? AF_INET : AF_INET6);
-      tail->next = node.release();
-      tail = tail->next;
-    }
-  }
-
-  return root.next;
-}
-
-#endif // HAVE_ARES_ADDR_NODE
-
 } // namespace aria2
diff --git a/src/AsyncNameResolver.h b/src/AsyncNameResolver.h
index 31a6ebe9..cc19260e 100644
--- a/src/AsyncNameResolver.h
+++ b/src/AsyncNameResolver.h
@@ -46,9 +46,14 @@
 
 namespace aria2 {
 
+struct AsyncNameResolverSocketEntry {
+  ares_socket_t fd;
+  int events;
+};
+
 class AsyncNameResolver {
   friend void callback(void* arg, int status, int timeouts,
-                       struct hostent* host);
+                       ares_addrinfo* result);
 
 public:
   enum STATUS {
@@ -59,6 +64,7 @@ public:
   };
 
 private:
+  std::vector<AsyncNameResolverSocketEntry> socks_;
   STATUS status_;
   int family_;
   ares_channel channel_;
@@ -68,12 +74,7 @@ private:
   std::string hostname_;
 
 public:
-  AsyncNameResolver(int family
-#ifdef HAVE_ARES_ADDR_NODE
-                    ,
-                    ares_addr_node* servers
-#endif // HAVE_ARES_ADDR_NODE
-  );
+  AsyncNameResolver(int family, const std::string& servers);
 
   ~AsyncNameResolver();
 
@@ -88,14 +89,14 @@ public:
 
   STATUS getStatus() const { return status_; }
 
-  int getFds(fd_set* rfdsPtr, fd_set* wfdsPtr) const;
+  ares_socket_t getFds(fd_set* rfdsPtr, fd_set* wfdsPtr) const;
 
   void process(fd_set* rfdsPtr, fd_set* wfdsPtr);
 
   int getFamily() const { return family_; }
 #ifdef HAVE_LIBCARES
 
-  int getsock(sock_t* sockets) const;
+  const std::vector<AsyncNameResolverSocketEntry>& getsock() const;
 
   void process(ares_socket_t readfd, ares_socket_t writefd);
 
@@ -105,17 +106,11 @@ public:
 
   void setAddr(const std::string& addrString);
 
-  void reset();
-
   const std::string& getHostname() const { return hostname_; }
+
+  void handle_sock_state(ares_socket_t sock, int read, int write);
 };
 
-#ifdef HAVE_ARES_ADDR_NODE
-
-ares_addr_node* parseAsyncDNSServers(const std::string& serversOpt);
-
-#endif // HAVE_ARES_ADDR_NODE
-
 } // namespace aria2
 
 #endif // D_ASYNC_NAME_RESOLVER_H
diff --git a/src/AsyncNameResolverMan.cc b/src/AsyncNameResolverMan.cc
index be073561..a9cb428c 100644
--- a/src/AsyncNameResolverMan.cc
+++ b/src/AsyncNameResolverMan.cc
@@ -88,12 +88,7 @@ void AsyncNameResolverMan::startAsyncFamily(const std::string& hostname,
                                             Command* command)
 {
   asyncNameResolver_[numResolver_] =
-      std::make_shared<AsyncNameResolver>(family
-#ifdef HAVE_ARES_ADDR_NODE
-                                          ,
-                                          e->getAsyncDNSServers()
-#endif // HAVE_ARES_ADDR_NODE
-      );
+      std::make_shared<AsyncNameResolver>(family, servers_);
   asyncNameResolver_[numResolver_]->resolve(hostname);
   setNameResolverCheck(numResolver_, e, command);
 }
@@ -222,6 +217,7 @@ void configureAsyncNameResolverMan(AsyncNameResolverMan* asyncNameResolverMan,
   if (!net::getIPv6AddrConfigured() || option->getAsBool(PREF_DISABLE_IPV6)) {
     asyncNameResolverMan->setIPv6(false);
   }
+  asyncNameResolverMan->setServers(option->get(PREF_ASYNC_DNS_SERVER));
 }
 
 } // namespace aria2
diff --git a/src/AsyncNameResolverMan.h b/src/AsyncNameResolverMan.h
index 617474ec..b3133b98 100644
--- a/src/AsyncNameResolverMan.h
+++ b/src/AsyncNameResolverMan.h
@@ -79,6 +79,8 @@ public:
   // Resets state. Also removes resolvers from DownloadEngine.
   void reset(DownloadEngine* e, Command* command);
 
+  void setServers(std::string servers) { servers_ = std::move(servers); }
+
 private:
   void startAsyncFamily(const std::string& hostname, int family,
                         DownloadEngine* e, Command* command);
@@ -88,6 +90,7 @@ private:
                                 Command* command);
 
   std::shared_ptr<AsyncNameResolver> asyncNameResolver_[2];
+  std::string servers_;
   size_t numResolver_;
   int resolverCheck_;
   bool ipv4_;
diff --git a/src/DownloadEngine.cc b/src/DownloadEngine.cc
index 2037f66f..8f392d11 100644
--- a/src/DownloadEngine.cc
+++ b/src/DownloadEngine.cc
@@ -104,9 +104,6 @@ DownloadEngine::DownloadEngine(std::unique_ptr<EventPoll> eventPoll)
 #ifdef ENABLE_BITTORRENT
       btRegistry_(make_unique<BtRegistry>()),
 #endif // ENABLE_BITTORRENT
-#ifdef HAVE_ARES_ADDR_NODE
-      asyncDNSServers_(nullptr),
-#endif // HAVE_ARES_ADDR_NODE
       dnsCache_(make_unique<DNSCache>()),
       option_(nullptr)
 {
@@ -115,12 +112,7 @@ DownloadEngine::DownloadEngine(std::unique_ptr<EventPoll> eventPoll)
   sessionId_.assign(&sessionId[0], &sessionId[sizeof(sessionId)]);
 }
 
-DownloadEngine::~DownloadEngine()
-{
-#ifdef HAVE_ARES_ADDR_NODE
-  setAsyncDNSServers(nullptr);
-#endif // HAVE_ARES_ADDR_NODE
-}
+DownloadEngine::~DownloadEngine() {}
 
 namespace {
 void executeCommand(std::deque<std::unique_ptr<Command>>& commands,
@@ -612,19 +604,6 @@ void DownloadEngine::setCheckIntegrityMan(
   checkIntegrityMan_ = std::move(ciman);
 }
 
-#ifdef HAVE_ARES_ADDR_NODE
-void DownloadEngine::setAsyncDNSServers(ares_addr_node* asyncDNSServers)
-{
-  ares_addr_node* node = asyncDNSServers_;
-  while (node) {
-    ares_addr_node* next = node->next;
-    delete node;
-    node = next;
-  }
-  asyncDNSServers_ = asyncDNSServers;
-}
-#endif // HAVE_ARES_ADDR_NODE
-
 #ifdef ENABLE_WEBSOCKET
 void DownloadEngine::setWebSocketSessionMan(
     std::unique_ptr<rpc::WebSocketSessionMan> wsman)
diff --git a/src/DownloadEngine.h b/src/DownloadEngine.h
index b544cfc6..c1c655c8 100644
--- a/src/DownloadEngine.h
+++ b/src/DownloadEngine.h
@@ -137,10 +137,6 @@ private:
 
   CUIDCounter cuidCounter_;
 
-#ifdef HAVE_ARES_ADDR_NODE
-  ares_addr_node* asyncDNSServers_;
-#endif // HAVE_ARES_ADDR_NODE
-
   std::unique_ptr<DNSCache> dnsCache_;
 
   std::unique_ptr<AuthConfigFactory> authConfigFactory_;
@@ -326,12 +322,6 @@ public:
 
   const std::string getSessionId() const { return sessionId_; }
 
-#ifdef HAVE_ARES_ADDR_NODE
-  void setAsyncDNSServers(ares_addr_node* asyncDNSServers);
-
-  ares_addr_node* getAsyncDNSServers() const { return asyncDNSServers_; }
-#endif // HAVE_ARES_ADDR_NODE
-
 #ifdef ENABLE_WEBSOCKET
   void setWebSocketSessionMan(std::unique_ptr<rpc::WebSocketSessionMan> wsman);
   const std::unique_ptr<rpc::WebSocketSessionMan>&
diff --git a/src/Event.h b/src/Event.h
index df8c4387..163552cf 100644
--- a/src/Event.h
+++ b/src/Event.h
@@ -293,16 +293,12 @@ private:
 
   Command* command_;
 
-  size_t socketsSize_;
-
-  sock_t sockets_[ARES_GETSOCK_MAXNUM];
+  std::vector<sock_t> sockets_;
 
 public:
   AsyncNameResolverEntry(std::shared_ptr<AsyncNameResolver> nameResolver,
                          Command* command)
-      : nameResolver_(std::move(nameResolver)),
-        command_(command),
-        socketsSize_(0)
+      : nameResolver_(std::move(nameResolver)), command_(command)
   {
   }
 
@@ -323,33 +319,27 @@ public:
 
   void addSocketEvents(EventPoll* e)
   {
-    socketsSize_ = 0;
-    int mask = nameResolver_->getsock(sockets_);
-    if (mask == 0) {
-      return;
-    }
-    size_t i;
-    for (i = 0; i < ARES_GETSOCK_MAXNUM; ++i) {
+    const auto& socks = nameResolver_->getsock();
+    sockets_.resize(socks.size());
+    auto sock_it = std::begin(sockets_);
+
+    for (const auto& ent : socks) {
       int events = 0;
-      if (ARES_GETSOCK_READABLE(mask, i)) {
+      if (ent.events & EventPoll::EVENT_READ) {
         events |= EventPoll::IEV_READ;
       }
-      if (ARES_GETSOCK_WRITABLE(mask, i)) {
+      if (ent.events & EventPoll::EVENT_WRITE) {
         events |= EventPoll::IEV_WRITE;
       }
-      if (events == 0) {
-        // assume no further sockets are returned.
-        break;
-      }
-      e->addEvents(sockets_[i], command_, events, nameResolver_);
+      e->addEvents(ent.fd, command_, events, nameResolver_);
+      *sock_it++ = ent.fd;
     }
-    socketsSize_ = i;
   }
 
   void removeSocketEvents(EventPoll* e)
   {
-    for (size_t i = 0; i < socketsSize_; ++i) {
-      e->deleteEvents(sockets_[i], command_, nameResolver_);
+    for (auto fd : sockets_) {
+      e->deleteEvents(fd, command_, nameResolver_);
     }
   }
 
diff --git a/src/InternalDHKeyExchange.cc b/src/InternalDHKeyExchange.cc
index 83058f5e..ccd69415 100644
--- a/src/InternalDHKeyExchange.cc
+++ b/src/InternalDHKeyExchange.cc
@@ -55,7 +55,7 @@ void DHKeyExchange::init(const unsigned char* prime, size_t primeBits,
   if (pr.empty()) {
     throw DL_ABORT_EX("No valid prime supplied");
   }
-  prime_ = n(pr.c_str(), pr.length());
+  prime_ = n(reinterpret_cast<const unsigned char*>(pr.c_str()), pr.length());
 
   std::string gen = reinterpret_cast<const char*>(generator);
   if (gen.length() % 2) {
@@ -65,12 +65,13 @@ void DHKeyExchange::init(const unsigned char* prime, size_t primeBits,
   if (gen.empty()) {
     throw DL_ABORT_EX("No valid generator supplied");
   }
-  generator_ = n(gen.c_str(), gen.length());
+  generator_ =
+      n(reinterpret_cast<const unsigned char*>(gen.c_str()), gen.length());
 
   size_t pbytes = (privateKeyBits + 7) / 8;
   unsigned char buf[pbytes];
   util::generateRandomData(buf, pbytes);
-  privateKey_ = n(reinterpret_cast<char*>(buf), pbytes);
+  privateKey_ = n(buf, pbytes);
 
   keyLength_ = (primeBits + 7) / 8;
 }
@@ -88,7 +89,7 @@ size_t DHKeyExchange::getPublicKey(unsigned char* out, size_t outLength) const
             static_cast<unsigned long>(keyLength_),
             static_cast<unsigned long>(outLength)));
   }
-  publicKey_.binary(reinterpret_cast<char*>(out), outLength);
+  publicKey_.binary(out, outLength);
   return keyLength_;
 }
 
@@ -114,10 +115,9 @@ size_t DHKeyExchange::computeSecret(unsigned char* out, size_t outLength,
             static_cast<unsigned long>(peerPublicKeyLength)));
   }
 
-  n peerKey(reinterpret_cast<const char*>(peerPublicKeyData),
-            peerPublicKeyLength);
+  n peerKey(peerPublicKeyData, peerPublicKeyLength);
   n secret = peerKey.mul_mod(privateKey_, prime_);
-  secret.binary(reinterpret_cast<char*>(out), outLength);
+  secret.binary(out, outLength);
 
   return outLength;
 }
diff --git a/src/MultiUrlRequestInfo.cc b/src/MultiUrlRequestInfo.cc
index 833188e3..46396f9c 100644
--- a/src/MultiUrlRequestInfo.cc
+++ b/src/MultiUrlRequestInfo.cc
@@ -272,11 +272,6 @@ int MultiUrlRequestInfo::prepare()
     clTlsContext->setVerifyPeer(option_->getAsBool(PREF_CHECK_CERTIFICATE));
     SocketCore::setClientTLSContext(clTlsContext);
 #endif
-#ifdef HAVE_ARES_ADDR_NODE
-    ares_addr_node* asyncDNSServers =
-        parseAsyncDNSServers(option_->get(PREF_ASYNC_DNS_SERVER));
-    e_->setAsyncDNSServers(asyncDNSServers);
-#endif // HAVE_ARES_ADDR_NODE
 
     std::string serverStatIf = option_->get(PREF_SERVER_STAT_IF);
     if (!serverStatIf.empty()) {
diff --git a/src/OptionHandlerFactory.cc b/src/OptionHandlerFactory.cc
index 2cd2c43e..000426b6 100644
--- a/src/OptionHandlerFactory.cc
+++ b/src/OptionHandlerFactory.cc
@@ -99,15 +99,13 @@ std::vector<OptionHandler*> OptionHandlerFactory::createOptionHandlers()
     op->setChangeOptionForReserved(true);
     handlers.push_back(op);
   }
-#  if defined(HAVE_ARES_SET_SERVERS) && defined(HAVE_ARES_ADDR_NODE)
   {
     OptionHandler* op(new DefaultOptionHandler(
         PREF_ASYNC_DNS_SERVER, TEXT_ASYNC_DNS_SERVER, NO_DEFAULT_VALUE));
     op->addTag(TAG_ADVANCED);
     handlers.push_back(op);
   }
-#  endif // HAVE_ARES_SET_SERVERS && HAVE_ARES_ADDR_NODE
-#endif   // ENABLE_ASYNC_DNS
+#endif // ENABLE_ASYNC_DNS
   {
     OptionHandler* op(new BooleanOptionHandler(
         PREF_AUTO_FILE_RENAMING, TEXT_AUTO_FILE_RENAMING, A2_V_TRUE,
diff --git a/src/SSHSession.cc b/src/SSHSession.cc
index 5f1ac4b0..5b299206 100644
--- a/src/SSHSession.cc
+++ b/src/SSHSession.cc
@@ -143,7 +143,7 @@ int SSHSession::checkDirection()
 
 ssize_t SSHSession::writeData(const void* data, size_t len)
 {
-  // net implemented yet
+  // not implemented yet
   assert(0);
 }
 
diff --git a/src/SelectEventPoll.cc b/src/SelectEventPoll.cc
index d9397b20..42943ac0 100644
--- a/src/SelectEventPoll.cc
+++ b/src/SelectEventPoll.cc
@@ -129,8 +129,8 @@ SelectEventPoll::AsyncNameResolverEntry::AsyncNameResolverEntry(
 {
 }
 
-int SelectEventPoll::AsyncNameResolverEntry::getFds(fd_set* rfdsPtr,
-                                                    fd_set* wfdsPtr)
+ares_socket_t SelectEventPoll::AsyncNameResolverEntry::getFds(fd_set* rfdsPtr,
+                                                              fd_set* wfdsPtr)
 {
   return nameResolver_->getFds(rfdsPtr, wfdsPtr);
 }
@@ -184,7 +184,7 @@ void SelectEventPoll::poll(const struct timeval& tv)
 
   for (auto& i : nameResolverEntries_) {
     auto& entry = i.second;
-    int fd = entry.getFds(&rfds, &wfds);
+    auto fd = entry.getFds(&rfds, &wfds);
     // TODO force error if fd == 0
     if (fdmax_ < fd) {
       fdmax_ = fd;
diff --git a/src/SelectEventPoll.h b/src/SelectEventPoll.h
index c09f423f..bb7a2da2 100644
--- a/src/SelectEventPoll.h
+++ b/src/SelectEventPoll.h
@@ -142,7 +142,7 @@ private:
               command_ < entry.command_);
     }
 
-    int getFds(fd_set* rfdsPtr, fd_set* wfdsPtr);
+    ares_socket_t getFds(fd_set* rfdsPtr, fd_set* wfdsPtr);
 
     void process(fd_set* rfdsPtr, fd_set* wfdsPtr);
   };
diff --git a/src/bignum.h b/src/bignum.h
index 5fb4402b..94a84a56 100644
--- a/src/bignum.h
+++ b/src/bignum.h
@@ -30,20 +30,20 @@ public:
   typedef std::make_unsigned<char_t>::type uchar_t;
 
 private:
-  std::unique_ptr<char_t[]> buf_;
+  std::unique_ptr<uchar_t[]> buf_;
 
 public:
-  inline ulong() : buf_(aria2::make_unique<char_t[]>(dim)) {}
-  inline ulong(size_t t) : buf_(aria2::make_unique<char_t[]>(dim))
+  inline ulong() : buf_(aria2::make_unique<uchar_t[]>(dim)) {}
+  inline ulong(size_t t) : buf_(aria2::make_unique<uchar_t[]>(dim))
   {
-    memcpy(buf_.get(), (char_t*)&t, sizeof(t));
+    memcpy(buf_.get(), (uchar_t*)&t, sizeof(t));
   }
-  inline ulong(const ulong<dim>& rhs) : buf_(aria2::make_unique<char_t[]>(dim))
+  inline ulong(const ulong<dim>& rhs) : buf_(aria2::make_unique<uchar_t[]>(dim))
   {
     memcpy(buf_.get(), rhs.buf_.get(), dim);
   }
-  explicit inline ulong(const char_t* data, size_t size)
-      : buf_(aria2::make_unique<char_t[]>(dim))
+  explicit inline ulong(const uchar_t* data, size_t size)
+      : buf_(aria2::make_unique<uchar_t[]>(dim))
   {
     if (size > dim) {
       throw std::bad_alloc();
@@ -73,8 +73,8 @@ public:
     const auto b2 = rhs.buf_.get();
     for (ssize_t i = dim - 1; i >= 0; --i) {
       for (ssize_t j = 1; j >= 0; --j) {
-        char_t t = ((uchar_t)(b1[i] << 4 * (1 - j))) >> 4;
-        char_t r = ((uchar_t)(b2[i] << 4 * (1 - j))) >> 4;
+        uchar_t t = ((uchar_t)(b1[i] << 4 * (1 - j))) >> 4;
+        uchar_t r = ((uchar_t)(b2[i] << 4 * (1 - j))) >> 4;
         if (t != r) {
           return t > r;
         }
@@ -101,8 +101,8 @@ public:
     bool base = false;
     for (size_t i = 0; i < dim; ++i) {
       for (ssize_t j = 0; j < 2; ++j) {
-        char_t t = ((uchar_t)(b1[i] << 4 * (1 - j))) >> 4;
-        char_t r = ((uchar_t)(b2[i] << 4 * (1 - j))) >> 4;
+        uchar_t t = ((uchar_t)(b1[i] << 4 * (1 - j))) >> 4;
+        uchar_t r = ((uchar_t)(b2[i] << 4 * (1 - j))) >> 4;
         if (base) {
           t++;
         }
@@ -144,8 +144,8 @@ public:
     bool base = false;
     for (size_t i = 0; i < dim; ++i) {
       for (ssize_t j = 0; j < 2; ++j) {
-        char_t t = ((uchar_t)(b1[i] << 4 * (1 - j))) >> 4;
-        char_t r = ((uchar_t)(b2[i] << 4 * (1 - j))) >> 4;
+        uchar_t t = ((uchar_t)(b1[i] << 4 * (1 - j))) >> 4;
+        uchar_t r = ((uchar_t)(b2[i] << 4 * (1 - j))) >> 4;
         if (base) {
           t--;
         }
@@ -238,14 +238,14 @@ public:
     return rv;
   }
 
-  std::unique_ptr<char_t[]> binary() const
+  std::unique_ptr<uchar_t[]> binary() const
   {
     ulong<dim> c = *this;
-    std::unique_ptr<char_t[]> rv;
+    std::unique_ptr<uchar_t[]> rv;
     rv.swap(c.buf_);
     return rv;
   }
-  void binary(char_t* buf, size_t len) const
+  void binary(uchar_t* buf, size_t len) const
   {
     memcpy(buf, buf_.get(), std::min(dim, len));
   }
@@ -258,8 +258,8 @@ private:
     size_t rv = dim * 2;
     const auto b = buf_.get();
     for (ssize_t i = dim - 1; i >= 0; --i) {
-      char_t f = b[i] >> 4;
-      char_t s = (b[i] << 4) >> 4;
+      uchar_t f = b[i] >> 4;
+      uchar_t s = (b[i] << 4) >> 4;
       if (!f && !s) {
         rv -= 2;
         continue;
@@ -282,8 +282,8 @@ private:
     const size_t d2 = digits / 2;
     for (size_t i = d2; i < dim; ++i) {
       for (size_t j = 0; j < 2; ++j) {
-        char_t c = ((uchar_t)(bt[(dim - 1) - i] << 4 * (1 - j))) >> 4;
-        char_t r = c << (npar * (1 - j) * 4 + (1 - npar) * j * 4);
+        uchar_t c = ((uchar_t)(bt[(dim - 1) - i] << 4 * (1 - j))) >> 4;
+        uchar_t r = c << (npar * (1 - j) * 4 + (1 - npar) * j * 4);
         ssize_t idx = i - d2 - npar * j;
         if (idx >= 0) {
           b[(dim - 1) - idx] += r;
diff --git a/src/option_processing.cc b/src/option_processing.cc
index a671b23a..d95ce753 100644
--- a/src/option_processing.cc
+++ b/src/option_processing.cc
@@ -103,10 +103,10 @@ int levenshtein(const char* a, const char* b, int swapcost, int subcost,
   int blen = strlen(b);
   std::vector<std::vector<int>> dp(3, std::vector<int>(blen + 1));
   for (int i = 0; i <= blen; ++i) {
-    dp[1][i] = i;
+    dp[1][i] = i * addcost;
   }
   for (int i = 1; i <= alen; ++i) {
-    dp[0][0] = i;
+    dp[0][0] = i * delcost;
     for (int j = 1; j <= blen; ++j) {
       dp[0][j] = dp[1][j - 1] + (a[i - 1] == b[j - 1] ? 0 : subcost);
       if (i >= 2 && j >= 2 && a[i - 1] != b[j - 1] && a[i - 2] == b[j - 1] &&
@@ -148,7 +148,7 @@ void showCandidates(const std::string& unknownOption,
       continue;
     }
     // cost values are borrowed from git, help.c.
-    int sim = levenshtein(optstr, pref->k, 0, 2, 1, 4);
+    int sim = levenshtein(optstr, pref->k, 0, 2, 1, 3);
     cands.push_back(std::make_pair(sim, pref));
   }
   if (cands.empty()) {
diff --git a/test/AsyncNameResolverTest.cc b/test/AsyncNameResolverTest.cc
index 0c793bc8..23518d37 100644
--- a/test/AsyncNameResolverTest.cc
+++ b/test/AsyncNameResolverTest.cc
@@ -11,43 +11,14 @@ namespace aria2 {
 class AsyncNameResolverTest : public CppUnit::TestFixture {
 
   CPPUNIT_TEST_SUITE(AsyncNameResolverTest);
-  CPPUNIT_TEST(testParseAsyncDNSServers);
   CPPUNIT_TEST_SUITE_END();
 
 public:
   void setUp() {}
 
   void tearDown() {}
-
-  void testParseAsyncDNSServers();
 };
 
 CPPUNIT_TEST_SUITE_REGISTRATION(AsyncNameResolverTest);
 
-void AsyncNameResolverTest::testParseAsyncDNSServers()
-{
-#ifdef HAVE_ARES_ADDR_NODE
-  in_addr ans4;
-  CPPUNIT_ASSERT_EQUAL((size_t)4, net::getBinAddr(&ans4, "192.168.0.1"));
-  in6_addr ans6;
-  CPPUNIT_ASSERT_EQUAL((size_t)16, net::getBinAddr(&ans6, "2001:db8::2:1"));
-
-  ares_addr_node* root;
-  root = parseAsyncDNSServers("192.168.0.1,2001:db8::2:1");
-  ares_addr_node* node = root;
-  CPPUNIT_ASSERT(node);
-  CPPUNIT_ASSERT_EQUAL(AF_INET, node->family);
-  CPPUNIT_ASSERT(memcmp(&ans4, &node->addr, sizeof(ans4)) == 0);
-  node = node->next;
-  CPPUNIT_ASSERT(node);
-  CPPUNIT_ASSERT_EQUAL(AF_INET6, node->family);
-  CPPUNIT_ASSERT(memcmp(&ans6, &node->addr, sizeof(ans6)) == 0);
-  for (node = root; node;) {
-    ares_addr_node* nextNode = node->next;
-    delete node;
-    node = nextNode;
-  }
-#endif // HAVE_ARES_ADDR_NODE
-}
-
 } // namespace aria2