diff --git a/tdutils/td/utils/config.h.in b/tdutils/td/utils/config.h.in
index ce6edb16..85f7bba7 100644
--- a/tdutils/td/utils/config.h.in
+++ b/tdutils/td/utils/config.h.in
@@ -6,3 +6,4 @@
 #cmakedefine01 TD_HAVE_COROUTINES
 #cmakedefine01 TD_HAVE_ABSL
 #cmakedefine01 TD_HAVE_GETOPT
+#cmakedefine01 TD_FD_DEBUG
diff --git a/tdutils/td/utils/port/detail/Epoll.cpp b/tdutils/td/utils/port/detail/Epoll.cpp
index 0fa6eb53..5c371c52 100644
--- a/tdutils/td/utils/port/detail/Epoll.cpp
+++ b/tdutils/td/utils/port/detail/Epoll.cpp
@@ -71,7 +71,7 @@ void Epoll::unsubscribe(PollableFdRef fd_ref) {
   int err = epoll_ctl(epoll_fd, EPOLL_CTL_DEL, native_fd, nullptr);
   auto epoll_ctl_errno = errno;
   LOG_IF(FATAL, err == -1) << Status::PosixError(epoll_ctl_errno, "epoll_ctl DEL failed") << ", epoll_fd = " << epoll_fd
-                           << ", fd = " << native_fd;
+                           << ", fd = " << native_fd << fd.native_fd().validate();
 }
 
 void Epoll::unsubscribe_before_close(PollableFdRef fd) {
diff --git a/tdutils/td/utils/port/detail/KQueue.cpp b/tdutils/td/utils/port/detail/KQueue.cpp
index 3c474442..3e2c4509 100644
--- a/tdutils/td/utils/port/detail/KQueue.cpp
+++ b/tdutils/td/utils/port/detail/KQueue.cpp
@@ -21,37 +21,33 @@ char disable_linker_warning_about_empty_file_kqueue_cpp TD_UNUSED;
 namespace td {
 namespace detail {
 
-KQueue::KQueue() {
-  kq = -1;
-}
 KQueue::~KQueue() {
   clear();
 }
 void KQueue::init() {
-  kq = kqueue();
+  kq_ = NativeFd(kqueue());
   auto kqueue_errno = errno;
-  LOG_IF(FATAL, kq == -1) << Status::PosixError(kqueue_errno, "kqueue creation failed");
+  LOG_IF(FATAL, !kq_) << Status::PosixError(kqueue_errno, "kqueue creation failed");
 
   // TODO: const
-  events.resize(1000);
-  changes_n = 0;
+  events_.resize(1000);
+  changes_n_ = 0;
 }
 
 void KQueue::clear() {
-  if (kq == -1) {
+  if (!kq_) {
     return;
   }
-  events.clear();
-  close(kq);
-  kq = -1;
-  for (auto *list_node = list_root.next; list_node != &list_root;) {
+  events_.clear();
+  kq_.close();
+  for (auto *list_node = list_root_.next; list_node != &list_root_;) {
     auto pollable_fd = PollableFd::from_list_node(list_node);
     list_node = list_node->next;
   }
 }
 
 int KQueue::update(int nevents, const timespec *timeout, bool may_fail) {
-  int err = kevent(kq, &events[0], changes_n, &events[0], nevents, timeout);
+  int err = kevent(kq_.fd(), &events_[0], changes_n_, &events_[0], nevents, timeout);
   auto kevent_errno = errno;
 
   bool is_fatal_error = [&] {
@@ -65,7 +61,7 @@ int KQueue::update(int nevents, const timespec *timeout, bool may_fail) {
   }();
   LOG_IF(FATAL, is_fatal_error) << Status::PosixError(kevent_errno, "kevent failed");
 
-  changes_n = 0;
+  changes_n_ = 0;
   if (err < 0) {
     return 0;
   }
@@ -73,7 +69,7 @@ int KQueue::update(int nevents, const timespec *timeout, bool may_fail) {
 }
 
 void KQueue::flush_changes(bool may_fail) {
-  if (!changes_n) {
+  if (!changes_n_) {
     return;
   }
   int n = update(0, nullptr, may_fail);
@@ -82,18 +78,18 @@ void KQueue::flush_changes(bool may_fail) {
 
 void KQueue::add_change(std::uintptr_t ident, int16 filter, uint16 flags, uint32 fflags, std::intptr_t data,
                         void *udata) {
-  if (changes_n == static_cast<int>(events.size())) {
+  if (changes_n_ == static_cast<int>(events_.size())) {
     flush_changes();
   }
-  EV_SET(&events[changes_n], ident, filter, flags, fflags, data, udata);
+  EV_SET(&events_[changes_n_], ident, filter, flags, fflags, data, udata);
   VLOG(fd) << "Subscribe [fd:" << ident << "] [filter:" << filter << "] [udata: " << udata << "]";
-  changes_n++;
+  changes_n_++;
 }
 
 void KQueue::subscribe(PollableFd fd, PollFlags flags) {
   auto native_fd = fd.native_fd().fd();
   auto list_node = fd.release_as_list_node();
-  list_root.put(list_node);
+  list_root_.put(list_node);
   if (flags.can_read()) {
     add_change(native_fd, EVFILT_READ, EV_ADD | EV_CLEAR, 0, 0, list_node);
   }
@@ -103,10 +99,10 @@ void KQueue::subscribe(PollableFd fd, PollFlags flags) {
 }
 
 void KQueue::invalidate(int native_fd) {
-  for (int i = 0; i < changes_n; i++) {
-    if (events[i].ident == static_cast<std::uintptr_t>(native_fd)) {
-      changes_n--;
-      std::swap(events[i], events[changes_n]);
+  for (int i = 0; i < changes_n_; i++) {
+    if (events_[i].ident == static_cast<std::uintptr_t>(native_fd)) {
+      changes_n_--;
+      std::swap(events_[i], events_[changes_n_]);
       i--;
     }
   }
@@ -129,7 +125,7 @@ void KQueue::unsubscribe_before_close(PollableFdRef fd_ref) {
   invalidate(pollable_fd.native_fd().fd());
 
   // just to avoid O(changes_n ^ 2)
-  if (changes_n != 0) {
+  if (changes_n_ != 0) {
     flush_changes();
   }
 }
@@ -145,9 +141,9 @@ void KQueue::run(int timeout_ms) {
     timeout_ptr = &timeout_data;
   }
 
-  int n = update(static_cast<int>(events.size()), timeout_ptr);
+  int n = update(static_cast<int>(events_.size()), timeout_ptr);
   for (int i = 0; i < n; i++) {
-    struct kevent *event = &events[i];
+    struct kevent *event = &events_[i];
     PollFlags flags;
     if (event->filter == EVFILT_WRITE) {
       flags.add_flags(PollFlags::Write());
diff --git a/tdutils/td/utils/port/detail/KQueue.h b/tdutils/td/utils/port/detail/KQueue.h
index a000def6..d054ed36 100644
--- a/tdutils/td/utils/port/detail/KQueue.h
+++ b/tdutils/td/utils/port/detail/KQueue.h
@@ -27,7 +27,7 @@ namespace detail {
 
 class KQueue final : public PollBase {
  public:
-  KQueue();
+  KQueue() = default;
   KQueue(const KQueue &) = delete;
   KQueue &operator=(const KQueue &) = delete;
   KQueue(KQueue &&) = delete;
@@ -51,10 +51,10 @@ class KQueue final : public PollBase {
   }
 
  private:
-  vector<struct kevent> events;
-  int changes_n;
-  int kq;
-  ListNode list_root;
+  vector<struct kevent> events_;
+  int changes_n_;
+  NativeFd kq_;
+  ListNode list_root_;
 
   int update(int nevents, const timespec *timeout, bool may_fail = false);
 
diff --git a/tdutils/td/utils/port/detail/NativeFd.cpp b/tdutils/td/utils/port/detail/NativeFd.cpp
index c4773cee..b36cb55d 100644
--- a/tdutils/td/utils/port/detail/NativeFd.cpp
+++ b/tdutils/td/utils/port/detail/NativeFd.cpp
@@ -15,13 +15,98 @@
 #include <unistd.h>
 #endif
 
+#if TD_FD_DEBUG
+#include <set>
+#include <mutex>
+#endif
+
 namespace td {
 
+#if TD_FD_DEBUG
+class FdSet {
+ public:
+  void on_create_fd(NativeFd::Fd fd) {
+    CHECK(fd >= 0);
+    if (is_stdio(fd)) {
+      return;
+    }
+    std::unique_lock<std::mutex> guard(mutex_);
+    if (fds_.count(fd) > 1) {
+      LOG(FATAL) << "Create duplicated fd: " << fd;
+    }
+    fds_.insert(fd);
+  }
+
+  void on_release_fd(NativeFd::Fd fd) {
+    CHECK(fd >= 0);
+    if (is_stdio(fd)) {
+      return;
+    }
+    LOG(FATAL) << "Unexpected release of non stdio NativeFd: " << fd;
+  }
+
+  Status validate(NativeFd::Fd fd) {
+    if (fd < 0) {
+      return Status::Error(PSLICE() << "Invalid fd: " << fd);
+    }
+    if (is_stdio(fd)) {
+      return Status::OK();
+    }
+    std::unique_lock<std::mutex> guard(mutex_);
+    if (fds_.count(fd) != 1) {
+      return Status::Error(PSLICE() << "Unknown fd: " << fd);
+    }
+    return Status::OK();
+  }
+
+  void on_close_fd(NativeFd::Fd fd) {
+    CHECK(fd >= 0);
+    if (is_stdio(fd)) {
+      return;
+    }
+    std::unique_lock<std::mutex> guard(mutex_);
+    if (fds_.count(fd) != 1) {
+      LOG(FATAL) << "Close unknown fd: " << fd;
+    }
+    fds_.erase(fd);
+  }
+
+ private:
+  std::mutex mutex_;
+  std::set<NativeFd::Fd> fds_;
+
+  bool is_stdio(NativeFd::Fd fd) {
+    return fd >= 0 && fd <= 2;
+  }
+};
+
+namespace {
+FdSet &get_fd_set() {
+  static FdSet res;
+  return res;
+}
+}  // namespace
+
+#endif
+Status NativeFd::validate() const {
+#if TD_FD_DEBUG
+  return get_fd_set().validate(fd_.get());
+#else
+  return Status::OK();
+#endif
+}
+
 NativeFd::NativeFd(Fd fd) : fd_(fd) {
   VLOG(fd) << *this << " create";
+#if TD_FD_DEBUG
+  get_fd_set().on_create_fd(fd);
+#endif
 }
 
 NativeFd::NativeFd(Fd fd, bool nolog) : fd_(fd) {
+#if TD_FD_DEBUG
+  get_fd_set().on_create_fd(fd);
+#endif
 }
 
 #if TD_PORT_WINDOWS
@@ -29,6 +114,14 @@ NativeFd::NativeFd(Socket socket) : fd_(reinterpret_cast<Fd>(socket)), is_socket
   VLOG(fd) << *this << " create";
 }
 #endif
+NativeFd &NativeFd::operator=(NativeFd &&from) {
+  close();
+  fd_ = std::move(from.fd_);
+#if TD_PORT_WINDOWS
+  is_socket_ = from.is_socket_;
+#endif
+  return *this;
+}
 
 NativeFd::~NativeFd() {
   close();
@@ -105,6 +198,11 @@ void NativeFd::close() {
   if (!*this) {
     return;
   }
+
+#if TD_FD_DEBUG
+  get_fd_set().on_close_fd(fd());
+#endif
+
   VLOG(fd) << *this << " close";
 #if TD_PORT_WINDOWS
   if (is_socket_ ? closesocket(socket()) : !CloseHandle(fd())) {
diff --git a/tdutils/td/utils/port/detail/NativeFd.h b/tdutils/td/utils/port/detail/NativeFd.h
index 38201f5b..2a2085ac 100644
--- a/tdutils/td/utils/port/detail/NativeFd.h
+++ b/tdutils/td/utils/port/detail/NativeFd.h
@@ -26,7 +26,7 @@ class NativeFd {
 #endif
   NativeFd() = default;
   NativeFd(NativeFd &&) = default;
-  NativeFd &operator=(NativeFd &&) = default;
+  NativeFd &operator=(NativeFd &&);
   explicit NativeFd(Fd fd);
   NativeFd(Fd fd, bool nolog);
 #if TD_PORT_WINDOWS
@@ -52,6 +52,8 @@ class NativeFd {
   void close();
   Fd release();
 
+  Status validate() const;
+
  private:
 #if TD_PORT_POSIX
   MovableValue<Fd, -1> fd_;