diff --git a/libtransmission/torrent.h b/libtransmission/torrent.h
index 7e7b08b2e..c1c50246c 100644
--- a/libtransmission/torrent.h
+++ b/libtransmission/torrent.h
@@ -1006,7 +1006,6 @@ private:
     friend tr_stat const* tr_torrentStat(tr_torrent* tor);
     friend tr_torrent* tr_torrentNew(tr_ctor* ctor, tr_torrent** setme_duplicate_of);
     friend uint64_t tr_torrentGetBytesLeftToAllocate(tr_torrent const* tor);
-    friend uint64_t tr_torrentGetBytesLeftToAllocate(tr_torrent const* tor);
 
     enum class VerifyState : uint8_t
     {
diff --git a/qt/ColumnResizer.cc b/qt/ColumnResizer.cc
index acbdbdb9d..8f5acaac2 100644
--- a/qt/ColumnResizer.cc
+++ b/qt/ColumnResizer.cc
@@ -42,7 +42,7 @@ ColumnResizer::ColumnResizer(QObject* parent)
 
 void ColumnResizer::addLayout(QGridLayout* layout)
 {
-    layouts_ << layout;
+    layouts_.emplace(layout);
     scheduleUpdate();
 }
 
diff --git a/qt/ColumnResizer.h b/qt/ColumnResizer.h
index 40f9cdd36..2d26e87f4 100644
--- a/qt/ColumnResizer.h
+++ b/qt/ColumnResizer.h
@@ -5,8 +5,9 @@
 
 #pragma once
 
+#include <set>
+
 #include <QObject>
-#include <QSet>
 #include <QTimer>
 
 #include <libtransmission/tr-macros.h>
@@ -33,5 +34,5 @@ private:
     void scheduleUpdate();
 
     QTimer timer_;
-    QSet<QGridLayout*> layouts_;
+    std::set<QGridLayout*> layouts_;
 };
diff --git a/qt/DetailsDialog.cc b/qt/DetailsDialog.cc
index 58c8d90f4..ab311b0e1 100644
--- a/qt/DetailsDialog.cc
+++ b/qt/DetailsDialog.cc
@@ -1428,19 +1428,20 @@ void DetailsDialog::onRemoveTrackerClicked()
     // make a map of torrentIds to announce URLs to remove
     QItemSelectionModel* selection_model = ui_.trackersView->selectionModel();
     QModelIndexList const selected_rows = selection_model->selectedRows();
-    QMultiMap<int, int> torrent_id_to_tracker_ids;
+    auto torrent_id_to_tracker_ids = std::map<int, std::set<int>>{};
 
-    for (QModelIndex const& i : selected_rows)
+    for (auto const& model_index : selected_rows)
     {
-        auto const inf = ui_.trackersView->model()->data(i, TrackerModel::TrackerRole).value<TrackerInfo>();
-        torrent_id_to_tracker_ids.insert(inf.torrent_id, inf.st.id);
+        auto const inf = ui_.trackersView->model()->data(model_index, TrackerModel::TrackerRole).value<TrackerInfo>();
+        torrent_id_to_tracker_ids[inf.torrent_id].insert(inf.st.id);
     }
 
     // batch all of a tracker's torrents into one command
-    for (int const id : torrent_id_to_tracker_ids.uniqueKeys())
+    for (auto const& [torrent_id, tracker_ids] : torrent_id_to_tracker_ids)
     {
-        torrent_ids_t const ids{ id };
-        torrentSet(ids, TR_KEY_trackerRemove, torrent_id_to_tracker_ids.values(id));
+        auto const ids = torrent_ids_t{ torrent_id };
+        auto const values = std::vector<int>{ std::begin(tracker_ids), std::end(tracker_ids) };
+        torrentSet(ids, TR_KEY_trackerRemove, values);
     }
 
     selection_model->clearSelection();
@@ -1582,15 +1583,15 @@ static constexpr tr_quark priorityKey(int priority)
     }
 }
 
-void DetailsDialog::onFilePriorityChanged(QSet<int> const& indices, int priority)
+void DetailsDialog::onFilePriorityChanged(file_indices_t const& indices, int priority)
 {
-    torrentSet(priorityKey(priority), indices.values());
+    torrentSet(priorityKey(priority), std::vector<int>{ std::begin(indices), std::end(indices) });
 }
 
-void DetailsDialog::onFileWantedChanged(QSet<int> const& indices, bool wanted)
+void DetailsDialog::onFileWantedChanged(file_indices_t const& indices, bool wanted)
 {
     tr_quark const key = wanted ? TR_KEY_files_wanted : TR_KEY_files_unwanted;
-    torrentSet(key, indices.values());
+    torrentSet(key, std::vector<int>{ std::begin(indices), std::end(indices) });
 }
 
 void DetailsDialog::onPathEdited(QString const& old_path, QString const& new_name)
diff --git a/qt/DetailsDialog.h b/qt/DetailsDialog.h
index a0c6be76a..e130370b1 100644
--- a/qt/DetailsDialog.h
+++ b/qt/DetailsDialog.h
@@ -10,7 +10,6 @@
 #include <unordered_set>
 
 #include <QString>
-#include <QSet>
 #include <QTimer>
 
 #include <libtransmission/tr-macros.h>
@@ -77,8 +76,8 @@ private slots:
     void onTrackerListEdited(QString);
 
     // Files tab
-    void onFilePriorityChanged(QSet<int> const& file_indices, int);
-    void onFileWantedChanged(QSet<int> const& file_indices, bool);
+    void onFilePriorityChanged(file_indices_t const& file_indices, int);
+    void onFileWantedChanged(file_indices_t const& file_indices, bool);
     void onPathEdited(QString const& old_path, QString const& new_name);
     void onOpenRequested(QString const& path) const;
 
diff --git a/qt/FileTreeItem.cc b/qt/FileTreeItem.cc
index 07db5ba7c..f96f17e2b 100644
--- a/qt/FileTreeItem.cc
+++ b/qt/FileTreeItem.cc
@@ -336,7 +336,7 @@ int FileTreeItem::priority() const
     return i;
 }
 
-void FileTreeItem::setSubtreePriority(int priority, QSet<int>& ids)
+void FileTreeItem::setSubtreePriority(int priority, file_indices_t& setme_changed_ids)
 {
     if (priority_ != priority)
     {
@@ -344,13 +344,13 @@ void FileTreeItem::setSubtreePriority(int priority, QSet<int>& ids)
 
         if (file_index_ >= 0)
         {
-            ids.insert(file_index_);
+            setme_changed_ids.insert(file_index_);
         }
     }
 
     for (FileTreeItem* const child : children_)
     {
-        child->setSubtreePriority(priority, ids);
+        child->setSubtreePriority(priority, setme_changed_ids);
     }
 }
 
@@ -386,21 +386,21 @@ int FileTreeItem::isSubtreeWanted() const
     return wanted;
 }
 
-void FileTreeItem::setSubtreeWanted(bool b, QSet<int>& ids)
+void FileTreeItem::setSubtreeWanted(bool wanted, file_indices_t& setme_changed_ids)
 {
-    if (is_wanted_ != b)
+    if (is_wanted_ != wanted)
     {
-        is_wanted_ = b;
+        is_wanted_ = wanted;
 
         if (file_index_ >= 0)
         {
-            ids.insert(file_index_);
+            setme_changed_ids.insert(file_index_);
         }
     }
 
     for (FileTreeItem* const child : children_)
     {
-        child->setSubtreeWanted(b, ids);
+        child->setSubtreeWanted(wanted, setme_changed_ids);
     }
 }
 
diff --git a/qt/FileTreeItem.h b/qt/FileTreeItem.h
index 0fab0e117..89a1d7b0e 100644
--- a/qt/FileTreeItem.h
+++ b/qt/FileTreeItem.h
@@ -10,13 +10,13 @@
 #include <vector>
 
 #include <QCoreApplication>
-#include <QSet>
 #include <QString>
 #include <QVariant>
 
 #include <libtransmission/tr-macros.h>
 
 #include "Utils.h" // for std::hash<QString>
+#include "Typedefs.h"
 
 class FileTreeItem
 {
@@ -69,8 +69,8 @@ public:
 
     QVariant data(int column, int role) const;
     std::pair<int, int> update(QString const& name, bool want, int priority, uint64_t have, bool update_fields);
-    void setSubtreeWanted(bool, QSet<int>& file_ids);
-    void setSubtreePriority(int priority, QSet<int>& file_ids);
+    void setSubtreeWanted(bool wanted, file_indices_t& setme_changed_ids);
+    void setSubtreePriority(int priority, file_indices_t& setme_changed_ids);
 
     [[nodiscard]] constexpr auto fileIndex() const noexcept
     {
diff --git a/qt/FileTreeModel.cc b/qt/FileTreeModel.cc
index f14630bae..2ad69a0b5 100644
--- a/qt/FileTreeModel.cc
+++ b/qt/FileTreeModel.cc
@@ -7,6 +7,7 @@
 #include <cassert>
 #include <map>
 #include <memory>
+#include <set>
 
 #include <libtransmission/transmission.h> // priorities
 
@@ -412,7 +413,7 @@ void FileTreeModel::emitParentsChanged(
     QModelIndex const& index,
     int first_column,
     int last_column,
-    QSet<QModelIndex>* visited_parent_indices)
+    std::set<QModelIndex>* visited_parent_indices)
 {
     assert(first_column <= last_column);
 
@@ -429,7 +430,7 @@ void FileTreeModel::emitParentsChanged(
 
         if (visited_parent_indices != nullptr)
         {
-            if (visited_parent_indices->contains(walk))
+            if (visited_parent_indices->count(walk) != 0U)
             {
                 break;
             }
@@ -525,7 +526,7 @@ void FileTreeModel::setWanted(QModelIndexList const& indices, bool wanted)
 
     QModelIndexList const orphan_indices = getOrphanIndices(indices);
 
-    QSet<int> file_ids;
+    auto file_ids = file_indices_t{};
 
     for (QModelIndex const& i : orphan_indices)
     {
@@ -537,14 +538,14 @@ void FileTreeModel::setWanted(QModelIndexList const& indices, bool wanted)
     }
 
     // emit parent changes separately to avoid multiple updates for same items
-    QSet<QModelIndex> parent_indices;
+    auto parent_indices = std::set<QModelIndex>{};
 
     for (QModelIndex const& i : orphan_indices)
     {
         emitParentsChanged(i, COL_SIZE, COL_WANTED, &parent_indices);
     }
 
-    if (!file_ids.isEmpty())
+    if (!std::empty(file_ids))
     {
         emit wantedChanged(file_ids, wanted);
     }
@@ -559,7 +560,7 @@ void FileTreeModel::setPriority(QModelIndexList const& indices, int priority)
 
     QModelIndexList const orphan_indices = getOrphanIndices(indices);
 
-    QSet<int> file_ids;
+    auto file_ids = file_indices_t{};
 
     for (QModelIndex const& i : orphan_indices)
     {
@@ -571,14 +572,13 @@ void FileTreeModel::setPriority(QModelIndexList const& indices, int priority)
     }
 
     // emit parent changes separately to avoid multiple updates for same items
-    QSet<QModelIndex> parent_indices;
-
+    auto parent_indices = std::set<QModelIndex>{};
     for (QModelIndex const& i : orphan_indices)
     {
         emitParentsChanged(i, COL_PRIORITY, COL_PRIORITY, &parent_indices);
     }
 
-    if (!file_ids.isEmpty())
+    if (!std::empty(file_ids))
     {
         emit priorityChanged(file_ids, priority);
     }
diff --git a/qt/FileTreeModel.h b/qt/FileTreeModel.h
index 9440fef0a..6cbc92c0a 100644
--- a/qt/FileTreeModel.h
+++ b/qt/FileTreeModel.h
@@ -8,12 +8,14 @@
 #include <cstdint> // uint64_t
 #include <map>
 #include <memory>
+#include <set>
 
 #include <QAbstractItemModel>
-#include <QSet>
 
 #include <libtransmission/tr-macros.h>
 
+#include "Typedefs.h" // file_indices_t
+
 class FileTreeItem;
 
 class FileTreeModel final : public QAbstractItemModel
@@ -77,8 +79,8 @@ public:
     bool setData(QModelIndex const& index, QVariant const& value, int role = Qt::EditRole) override;
 
 signals:
-    void priorityChanged(QSet<int> const& file_indices, int);
-    void wantedChanged(QSet<int> const& file_indices, bool);
+    void priorityChanged(file_indices_t const& file_indices, int);
+    void wantedChanged(file_indices_t const& file_indices, bool);
     void pathEdited(QString const& oldpath, QString const& new_name);
     void openRequested(QString const& path);
 
@@ -89,7 +91,7 @@ private:
         QModelIndex const&,
         int first_column,
         int last_column,
-        QSet<QModelIndex>* visited_parent_indices = nullptr);
+        std::set<QModelIndex>* visited_parent_indices = nullptr);
     void emitSubtreeChanged(QModelIndex const&, int first_column, int last_column);
     FileTreeItem* findItemForFileIndex(int file_index) const;
     FileTreeItem* itemFromIndex(QModelIndex const&) const;
diff --git a/qt/FileTreeView.cc b/qt/FileTreeView.cc
index 96dde6c0e..a2b5c9893 100644
--- a/qt/FileTreeView.cc
+++ b/qt/FileTreeView.cc
@@ -6,6 +6,7 @@
 #include <algorithm>
 #include <cassert>
 #include <queue>
+#include <set>
 
 #include <QHeaderView>
 #include <QMenu>
@@ -253,7 +254,7 @@ void FileTreeView::onlyCheckSelectedItems()
 
     std::sort(wanted_indices.begin(), wanted_indices.end());
 
-    QSet<QModelIndex> wanted_indices_parents;
+    auto wanted_indices_parents = std::set<QModelIndex>{};
 
     for (QModelIndex const& i : wanted_indices)
     {
@@ -294,7 +295,7 @@ void FileTreeView::onlyCheckSelectedItems()
             {
                 unwanted_indices << child_index;
             }
-            else if (!wanted_indices_parents.contains(child_index))
+            else if (wanted_indices_parents.count(child_index) == 0U)
             {
                 unwanted_indices << child_index;
             }
diff --git a/qt/FileTreeView.h b/qt/FileTreeView.h
index 1f16d79bc..cbfe2c813 100644
--- a/qt/FileTreeView.h
+++ b/qt/FileTreeView.h
@@ -5,12 +5,12 @@
 
 #pragma once
 
-#include <QSet>
 #include <QTreeView>
 
 #include <libtransmission/tr-macros.h>
 
 #include "Torrent.h" // FileList
+#include "Typedefs.h" // file_indices_t
 
 class QAction;
 class QMenu;
@@ -33,8 +33,8 @@ public:
     void setEditable(bool editable);
 
 signals:
-    void priorityChanged(QSet<int> const& file_indices, int priority);
-    void wantedChanged(QSet<int> const& file_indices, bool wanted);
+    void priorityChanged(file_indices_t const& file_indices, int priority);
+    void wantedChanged(file_indices_t const& file_indices, bool wanted);
     void pathEdited(QString const& old_path, QString const& new_name);
     void openRequested(QString const& path);
 
diff --git a/qt/OptionsDialog.cc b/qt/OptionsDialog.cc
index 44a083ef9..ce2cf6939 100644
--- a/qt/OptionsDialog.cc
+++ b/qt/OptionsDialog.cc
@@ -205,7 +205,7 @@ void OptionsDialog::onSessionUpdated()
     }
 }
 
-void OptionsDialog::onPriorityChanged(QSet<int> const& file_indices, int priority)
+void OptionsDialog::onPriorityChanged(file_indices_t const& file_indices, int priority)
 {
     for (int const i : file_indices)
     {
@@ -213,7 +213,7 @@ void OptionsDialog::onPriorityChanged(QSet<int> const& file_indices, int priorit
     }
 }
 
-void OptionsDialog::onWantedChanged(QSet<int> const& file_indices, bool is_wanted)
+void OptionsDialog::onWantedChanged(file_indices_t const& file_indices, bool is_wanted)
 {
     for (int const i : file_indices)
     {
diff --git a/qt/OptionsDialog.h b/qt/OptionsDialog.h
index 342ce3aa4..f35cd5bd6 100644
--- a/qt/OptionsDialog.h
+++ b/qt/OptionsDialog.h
@@ -11,7 +11,6 @@
 
 #include <QDir>
 #include <QFile>
-#include <QSet>
 #include <QString>
 #include <QTimer>
 
@@ -20,6 +19,7 @@
 #include "AddData.h" // AddData
 #include "BaseDialog.h"
 #include "Torrent.h" // FileList
+#include "Typedefs.h" // file_indices_t
 #include "ui_OptionsDialog.h"
 
 #include <libtransmission/transmission.h>
@@ -45,8 +45,8 @@ public:
 
 private slots:
     void onAccepted();
-    void onPriorityChanged(QSet<int> const& file_indices, int);
-    void onWantedChanged(QSet<int> const& file_indices, bool);
+    void onPriorityChanged(file_indices_t const& file_indices, int);
+    void onWantedChanged(file_indices_t const& file_indices, bool);
 
     void onSourceChanged();
     void onDestinationChanged();
diff --git a/qt/Prefs.cc b/qt/Prefs.cc
index d6fc0d60b..5b95d1daf 100644
--- a/qt/Prefs.cc
+++ b/qt/Prefs.cc
@@ -225,7 +225,7 @@ Prefs::Prefs(QString config_dir)
 
     // these are the prefs that don't get saved to settings.json
     // when the application exits.
-    temporary_prefs_ << FILTER_TEXT;
+    temporary_prefs_.insert(FILTER_TEXT);
 
     auto top = get_default_app_settings();
     top.merge(tr_sessionLoadSettings(config_dir_.toUtf8().constData(), nullptr));
@@ -326,7 +326,7 @@ Prefs::~Prefs()
 
     for (int i = 0; i < PREFS_COUNT; ++i)
     {
-        if (temporary_prefs_.contains(i))
+        if (temporary_prefs_.count(i) != 0U)
         {
             continue;
         }
diff --git a/qt/Prefs.h b/qt/Prefs.h
index b0e5165e6..9ac5b68b0 100644
--- a/qt/Prefs.h
+++ b/qt/Prefs.h
@@ -6,9 +6,9 @@
 #pragma once
 
 #include <array>
+#include <set>
 
 #include <QObject>
-#include <QSet>
 #include <QString>
 #include <QVariant>
 
@@ -204,7 +204,7 @@ private:
 
     QString const config_dir_;
 
-    QSet<int> temporary_prefs_;
+    std::set<int> temporary_prefs_;
     std::array<QVariant, PREFS_COUNT> mutable values_;
 
     static std::array<PrefItem, PREFS_COUNT> const Items;
diff --git a/qt/Session.cc b/qt/Session.cc
index a03e24541..2f5db906f 100644
--- a/qt/Session.cc
+++ b/qt/Session.cc
@@ -460,7 +460,7 @@ Session::Tag Session::torrentSet(torrent_ids_t const& torrent_ids, tr_quark cons
     return torrentSetImpl(&args);
 }
 
-Session::Tag Session::torrentSet(torrent_ids_t const& torrent_ids, tr_quark const key, QList<int> const& value)
+Session::Tag Session::torrentSet(torrent_ids_t const& torrent_ids, tr_quark const key, std::vector<int> const& value)
 {
     tr_variant args;
     tr_variantInitDict(&args, 2);
diff --git a/qt/Session.h b/qt/Session.h
index 6461e7456..07449af17 100644
--- a/qt/Session.h
+++ b/qt/Session.h
@@ -88,7 +88,7 @@ public:
     Tag torrentSet(torrent_ids_t const& torrent_ids, tr_quark const key, int val);
     Tag torrentSet(torrent_ids_t const& torrent_ids, tr_quark const key, double val);
     Tag torrentSet(torrent_ids_t const& torrent_ids, tr_quark const key, QString const& val);
-    Tag torrentSet(torrent_ids_t const& torrent_ids, tr_quark const key, QList<int> const& val);
+    Tag torrentSet(torrent_ids_t const& torrent_ids, tr_quark const key, std::vector<int> const& val);
     Tag torrentSet(torrent_ids_t const& torrent_ids, tr_quark const key, QStringList const& val);
 
     void torrentSetLocation(torrent_ids_t const& torrent_ids, QString const& path, bool do_move);
diff --git a/qt/Typedefs.h b/qt/Typedefs.h
index c142b37d7..601b14db6 100644
--- a/qt/Typedefs.h
+++ b/qt/Typedefs.h
@@ -1,7 +1,10 @@
 #pragma once
 
+#include <set>
 #include <unordered_set>
 
 #include <libtransmission/transmission.h>
 
 using torrent_ids_t = std::unordered_set<tr_torrent_id_t>;
+
+using file_indices_t = std::set<int>;
diff --git a/qt/WatchDir.cc b/qt/WatchDir.cc
index 3bb30b3c0..8bee4520f 100644
--- a/qt/WatchDir.cc
+++ b/qt/WatchDir.cc
@@ -76,51 +76,44 @@ void WatchDir::setPath(QString const& path, bool is_enabled)
 
 void WatchDir::watcherActivated(QString const& path)
 {
-    auto const dir = QDir{ path };
-
     // get the list of files currently in the watch directory
-    QSet<QString> files;
-
-    for (QString const& str : dir.entryList(QDir::Readable | QDir::Files))
-    {
-        files.insert(str);
-    }
+    auto const dir = QDir{ path };
+    auto const files = dir.entryList(QDir::Readable | QDir::Files);
 
     // try to add any new files which end in torrent
-    auto const new_files = files - watch_dir_files_;
     auto const torrent_suffix = QStringLiteral(".torrent");
-
-    for (QString const& name : new_files)
+    for (auto const& name : files)
     {
-        if (name.endsWith(torrent_suffix, Qt::CaseInsensitive))
+        if (!name.endsWith(torrent_suffix, Qt::CaseInsensitive) || (watch_dir_files_.count(name) != 0U))
         {
-            QString const filename = dir.absoluteFilePath(name);
+            continue;
+        }
 
-            switch (metainfoTest(filename))
+        auto const filename = dir.absoluteFilePath(name);
+        switch (metainfoTest(filename))
+        {
+        case AddResult::Success:
+            emit torrentFileAdded(filename);
+            break;
+
+        case AddResult::Duplicate:
+            break;
+
+        case AddResult::Error:
             {
-            case AddResult::Success:
-                emit torrentFileAdded(filename);
-                break;
-
-            case AddResult::Duplicate:
-                break;
-
-            case AddResult::Error:
-                {
-                    // give the torrent a few seconds to finish downloading
-                    auto* t = new QTimer{ this };
-                    t->setObjectName(dir.absoluteFilePath(name));
-                    t->setSingleShot(true);
-                    connect(t, &QTimer::timeout, this, &WatchDir::onTimeout);
-                    t->start(5000);
-                }
+                // give the torrent a few seconds to finish downloading
+                auto* t = new QTimer(this);
+                t->setObjectName(dir.absoluteFilePath(name));
+                t->setSingleShot(true);
+                connect(t, &QTimer::timeout, this, &WatchDir::onTimeout);
+                t->start(5000);
             }
         }
     }
 
     // update our file list so that we can use it
     // for comparison the next time around
-    watch_dir_files_ = files;
+    watch_dir_files_ = { std::begin(files), std::end(files) };
 }
 
 void WatchDir::rescanAllWatchedDirectories()
diff --git a/qt/WatchDir.h b/qt/WatchDir.h
index 4826983bd..8dcf436b7 100644
--- a/qt/WatchDir.h
+++ b/qt/WatchDir.h
@@ -6,10 +6,10 @@
 #pragma once
 
 #include <memory>
+#include <set>
 
 #include <QObject>
 #include <QFileSystemWatcher>
-#include <QSet>
 #include <QString>
 
 #include <libtransmission/tr-macros.h>
@@ -47,6 +47,6 @@ private:
 
     TorrentModel const& model_;
 
-    QSet<QString> watch_dir_files_;
+    std::set<QString> watch_dir_files_;
     std::unique_ptr<QFileSystemWatcher> watcher_;
 };