diff --git a/CMakeLists.txt b/CMakeLists.txt
index ec4597638..5c1e961cb 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -31,7 +31,6 @@ include(CheckCXXSourceCompiles)
 
 option(WITH_TESTS "Enable building of unit tests" ON)
 option(WITH_GUI_TESTS "Enable building of GUI tests" OFF)
-option(WITH_LTO "Enable Link Time Optimization (LTO)" OFF)
 
 set(KEEPASSX_VERSION "2.0 beta 2")
 set(KEEPASSX_VERSION_NUM "1.9.92")
@@ -100,20 +99,6 @@ if(CMAKE_SYSTEM_NAME STREQUAL "Linux")
   set(CMAKE_MODULE_LINKER_FLAGS "${CMAKE_MODULE_LINKER_FLAGS} -Wl,-z,relro")
 endif()
 
-if(WITH_LTO)
-  if(CMAKE_COMPILER_IS_GNUCC AND CMAKE_COMPILER_IS_GNUCXX)
-    check_cxx_compiler_flag("-flto -fuse-linker-plugin" LTO_AVAILABLE)
-
-    if(LTO_AVAILABLE)
-      add_gcc_compiler_flags("-flto -fuse-linker-plugin")
-    else()
-      message(FATAL_ERROR "This version of gcc doesn't support LTO")
-    endif(LTO_AVAILABLE)
-  else()
-    message(FATAL_ERROR "LTO is only supported with gcc")
-  endif()
-endif()
-
 add_gcc_compiler_cxxflags("-std=c++11")
 
 if(APPLE)
diff --git a/src/autotype/CMakeLists.txt b/src/autotype/CMakeLists.txt
index a129961e2..707edf910 100644
--- a/src/autotype/CMakeLists.txt
+++ b/src/autotype/CMakeLists.txt
@@ -5,7 +5,7 @@ if(UNIX AND NOT APPLE)
   add_feature_info(libXtest X11_XTest_FOUND "The X11 XTEST Protocol library is required for auto-type")
   add_feature_info(Qt5X11Extras Qt5X11Extras_FOUND "The Qt5X11Extras library is required for auto-type")
 
-  if(X11_FOUND AND X11_XTest_FOUND AND Qt5X11Extras_FOUND)
+  if(X11_FOUND AND X11_Xi_FOUND AND X11_XTest_FOUND AND Qt5X11Extras_FOUND)
     add_subdirectory(xcb)
   endif()
 endif()
diff --git a/src/autotype/test/AutoTypeTest.h b/src/autotype/test/AutoTypeTest.h
index be57af050..e7bd3a96a 100644
--- a/src/autotype/test/AutoTypeTest.h
+++ b/src/autotype/test/AutoTypeTest.h
@@ -33,23 +33,23 @@ class AutoTypePlatformTest : public QObject,
     Q_INTERFACES(AutoTypePlatformInterface AutoTypeTestInterface)
 
 public:
-    QString keyToString(Qt::Key key);
+    QString keyToString(Qt::Key key) Q_DECL_OVERRIDE;
 
-    QStringList windowTitles();
-    WId activeWindow();
-    QString activeWindowTitle();
-    bool registerGlobalShortcut(Qt::Key key, Qt::KeyboardModifiers modifiers);
-    void unregisterGlobalShortcut(Qt::Key key, Qt::KeyboardModifiers modifiers);
-    int platformEventFilter(void* event);
-    int initialTimeout();
-    bool raiseWindow(WId window);
-    AutoTypeExecutor* createExecutor();
+    QStringList windowTitles() Q_DECL_OVERRIDE;
+    WId activeWindow() Q_DECL_OVERRIDE;
+    QString activeWindowTitle() Q_DECL_OVERRIDE;
+    bool registerGlobalShortcut(Qt::Key key, Qt::KeyboardModifiers modifiers) Q_DECL_OVERRIDE;
+    void unregisterGlobalShortcut(Qt::Key key, Qt::KeyboardModifiers modifiers) Q_DECL_OVERRIDE;
+    int platformEventFilter(void* event) Q_DECL_OVERRIDE;
+    int initialTimeout() Q_DECL_OVERRIDE;
+    bool raiseWindow(WId window) Q_DECL_OVERRIDE;
+    AutoTypeExecutor* createExecutor() Q_DECL_OVERRIDE;
 
-    void setActiveWindowTitle(const QString& title);
+    void setActiveWindowTitle(const QString& title) Q_DECL_OVERRIDE;
 
-    QString actionChars();
-    int actionCount();
-    void clearActions();
+    QString actionChars() Q_DECL_OVERRIDE;
+    int actionCount() Q_DECL_OVERRIDE;
+    void clearActions() Q_DECL_OVERRIDE;
 
     void addActionChar(AutoTypeChar* action);
     void addActionKey(AutoTypeKey* action);
@@ -68,8 +68,8 @@ class AutoTypeExecturorTest : public AutoTypeExecutor
 public:
     explicit AutoTypeExecturorTest(AutoTypePlatformTest* platform);
 
-    void execChar(AutoTypeChar* action);
-    void execKey(AutoTypeKey* action);
+    void execChar(AutoTypeChar* action) Q_DECL_OVERRIDE;
+    void execKey(AutoTypeKey* action) Q_DECL_OVERRIDE;
 
 private:
     AutoTypePlatformTest* const m_platform;
diff --git a/src/autotype/xcb/AutoTypeXCB.cpp b/src/autotype/xcb/AutoTypeXCB.cpp
index 1a6d27d63..054aacb0a 100644
--- a/src/autotype/xcb/AutoTypeXCB.cpp
+++ b/src/autotype/xcb/AutoTypeXCB.cpp
@@ -31,12 +31,12 @@ AutoTypePlatformX11::AutoTypePlatformX11()
     m_dpy = QX11Info::display();
     m_rootWindow = QX11Info::appRootWindow();
 
-    m_atomWmState = XInternAtom(m_dpy, "WM_STATE", true);
-    m_atomWmName = XInternAtom(m_dpy, "WM_NAME", true);
-    m_atomNetWmName = XInternAtom(m_dpy, "_NET_WM_NAME", true);
-    m_atomString = XInternAtom(m_dpy, "STRING", true);
-    m_atomUtf8String = XInternAtom(m_dpy, "UTF8_STRING", true);
-    m_atomNetActiveWindow = XInternAtom(m_dpy, "_NET_ACTIVE_WINDOW", true);
+    m_atomWmState = XInternAtom(m_dpy, "WM_STATE", True);
+    m_atomWmName = XInternAtom(m_dpy, "WM_NAME", True);
+    m_atomNetWmName = XInternAtom(m_dpy, "_NET_WM_NAME", True);
+    m_atomString = XInternAtom(m_dpy, "STRING", True);
+    m_atomUtf8String = XInternAtom(m_dpy, "UTF8_STRING", True);
+    m_atomNetActiveWindow = XInternAtom(m_dpy, "_NET_ACTIVE_WINDOW", True);
 
     m_classBlacklist << "desktop_window" << "gnome-panel"; // Gnome
     m_classBlacklist << "kdesktop" << "kicker"; // KDE 3
@@ -118,12 +118,12 @@ bool AutoTypePlatformX11::registerGlobalShortcut(Qt::Key key, Qt::KeyboardModifi
     uint nativeModifiers = qtToNativeModifiers(modifiers);
 
     startCatchXErrors();
-    XGrabKey(m_dpy, keycode, nativeModifiers, m_rootWindow, true, GrabModeAsync, GrabModeAsync);
-    XGrabKey(m_dpy, keycode, nativeModifiers | Mod2Mask, m_rootWindow, true, GrabModeAsync,
+    XGrabKey(m_dpy, keycode, nativeModifiers, m_rootWindow, True, GrabModeAsync, GrabModeAsync);
+    XGrabKey(m_dpy, keycode, nativeModifiers | Mod2Mask, m_rootWindow, True, GrabModeAsync,
              GrabModeAsync);
-    XGrabKey(m_dpy, keycode, nativeModifiers | LockMask, m_rootWindow, true, GrabModeAsync,
+    XGrabKey(m_dpy, keycode, nativeModifiers | LockMask, m_rootWindow, True, GrabModeAsync,
              GrabModeAsync);
-    XGrabKey(m_dpy, keycode, nativeModifiers | Mod2Mask | LockMask, m_rootWindow, true,
+    XGrabKey(m_dpy, keycode, nativeModifiers | Mod2Mask | LockMask, m_rootWindow, True,
              GrabModeAsync, GrabModeAsync);
     stopCatchXErrors();
 
@@ -236,7 +236,7 @@ QString AutoTypePlatformX11::windowTitle(Window window, bool useBlacklist)
 
     // the window manager spec says we should read _NET_WM_NAME first, then fall back to WM_NAME
 
-    int retVal = XGetWindowProperty(m_dpy, window, m_atomNetWmName, 0, 1000, false, m_atomUtf8String,
+    int retVal = XGetWindowProperty(m_dpy, window, m_atomNetWmName, 0, 1000, False, m_atomUtf8String,
                                     &type, &format, &nitems, &after, &data);
 
     if ((retVal == 0) && data) {
@@ -359,7 +359,7 @@ bool AutoTypePlatformX11::isTopLevelWindow(Window window)
     unsigned long nitems;
     unsigned long after;
     unsigned char* data = nullptr;
-    int retVal = XGetWindowProperty(m_dpy, window, m_atomWmState, 0, 0, false, AnyPropertyType, &type, &format,
+    int retVal = XGetWindowProperty(m_dpy, window, m_atomWmState, 0, 0, False, AnyPropertyType, &type, &format,
                                     &nitems, &after, &data);
     if (data) {
         XFree(data);
@@ -541,7 +541,7 @@ void AutoTypePlatformX11::stopCatchXErrors()
 {
     Q_ASSERT(m_catchXErrors);
 
-    XSync(m_dpy, false);
+    XSync(m_dpy, False);
     XSetErrorHandler(m_oldXErrorHandler);
     m_catchXErrors = false;
 }
@@ -594,7 +594,14 @@ void AutoTypePlatformX11::SendEvent(XKeyEvent* event, int event_type)
     int (*oldHandler) (Display*, XErrorEvent*) = XSetErrorHandler(MyErrorHandler);
 
     event->type = event_type;
-    XTestFakeKeyEvent(event->display, event->keycode, event->type == KeyPress, 0);
+    Bool press;
+    if (event->type == KeyPress) {
+        press = True;
+    }
+    else {
+        press = False;
+    }
+    XTestFakeKeyEvent(event->display, event->keycode, press, 0);
     XFlush(event->display);
 
     XSetErrorHandler(oldHandler);
diff --git a/src/autotype/xcb/AutoTypeXCB.h b/src/autotype/xcb/AutoTypeXCB.h
index a924b9586..63764ba81 100644
--- a/src/autotype/xcb/AutoTypeXCB.h
+++ b/src/autotype/xcb/AutoTypeXCB.h
@@ -43,15 +43,15 @@ class AutoTypePlatformX11 : public QObject, public AutoTypePlatformInterface
 public:
     AutoTypePlatformX11();
     void unload() override;
-    QStringList windowTitles();
-    WId activeWindow();
-    QString activeWindowTitle();
-    bool registerGlobalShortcut(Qt::Key key, Qt::KeyboardModifiers modifiers);
-    void unregisterGlobalShortcut(Qt::Key key, Qt::KeyboardModifiers modifiers);
-    int platformEventFilter(void* event);
-    int initialTimeout();
-    bool raiseWindow(WId window);
-    AutoTypeExecutor* createExecutor();
+    QStringList windowTitles() override;
+    WId activeWindow() override;
+    QString activeWindowTitle() override;
+    bool registerGlobalShortcut(Qt::Key key, Qt::KeyboardModifiers modifiers) override;
+    void unregisterGlobalShortcut(Qt::Key key, Qt::KeyboardModifiers modifiers) override;
+    int platformEventFilter(void* event) override;
+    int initialTimeout() override;
+    bool raiseWindow(WId window) override;
+    AutoTypeExecutor* createExecutor() override;
 
     KeySym charToKeySym(const QChar& ch);
     KeySym keyToKeySym(Qt::Key key);
@@ -122,8 +122,8 @@ class AutoTypeExecturorX11 : public AutoTypeExecutor
 public:
     explicit AutoTypeExecturorX11(AutoTypePlatformX11* platform);
 
-    void execChar(AutoTypeChar* action);
-    void execKey(AutoTypeKey* action);
+    void execChar(AutoTypeChar* action) Q_DECL_OVERRIDE;
+    void execKey(AutoTypeKey* action) Q_DECL_OVERRIDE;
 
 private:
     AutoTypePlatformX11* const m_platform;
diff --git a/src/format/KeePass2Reader.cpp b/src/format/KeePass2Reader.cpp
index a3f58dd31..1aa5fee69 100644
--- a/src/format/KeePass2Reader.cpp
+++ b/src/format/KeePass2Reader.cpp
@@ -24,6 +24,7 @@
 #include "core/Database.h"
 #include "core/Endian.h"
 #include "crypto/CryptoHash.h"
+#include "format/KeePass1.h"
 #include "format/KeePass2.h"
 #include "format/KeePass2RandomStream.h"
 #include "format/KeePass2XmlReader.h"
@@ -70,7 +71,14 @@ Database* KeePass2Reader::readDatabase(QIODevice* device, const CompositeKey& ke
     }
 
     quint32 signature2 = Endian::readUInt32(m_headerStream, KeePass2::BYTEORDER, &ok);
-    if (!ok || signature2 != KeePass2::SIGNATURE_2) {
+    if (ok && signature2 == KeePass1::SIGNATURE_2) {
+        raiseError(tr("The selected file is an old KeePass 1 database (.kdb).\n\n"
+                      "You can import it by clicking on Database > 'Import KeePass 1 database'.\n"
+                      "This is a one-way migration. You won't be able to open the imported "
+                      "database with the old KeePassX 0.4 version."));
+        return Q_NULLPTR;
+    }
+    else if (!ok || signature2 != KeePass2::SIGNATURE_2) {
         raiseError(tr("Not a KeePass database."));
         return nullptr;
     }
diff --git a/src/gui/FileDialog.cpp b/src/gui/FileDialog.cpp
index 78a897f45..e293db2ba 100644
--- a/src/gui/FileDialog.cpp
+++ b/src/gui/FileDialog.cpp
@@ -67,6 +67,7 @@ QString FileDialog::getSaveFileName(QWidget* parent, const QString& caption, QSt
 
         QString result;
 #if defined(Q_OS_MAC) || defined(Q_OS_WIN)
+        Q_UNUSED(defaultExtension);
         // the native dialogs on these platforms already append the file extension
         result = QFileDialog::getSaveFileName(parent, caption, dir, filter,
                                               selectedFilter, options);
diff --git a/src/gui/entry/EntryModel.cpp b/src/gui/entry/EntryModel.cpp
index ae66298d9..d4419dd93 100644
--- a/src/gui/entry/EntryModel.cpp
+++ b/src/gui/entry/EntryModel.cpp
@@ -243,7 +243,7 @@ QMimeData* EntryModel::mimeData(const QModelIndexList& indexes) const
         return nullptr;
     }
     else {
-        data->setData(mimeTypes().first(), encoded);
+        data->setData(mimeTypes().at(0), encoded);
         return data;
     }
 }
diff --git a/src/gui/group/GroupModel.cpp b/src/gui/group/GroupModel.cpp
index 85314e2bd..b1aed4137 100644
--- a/src/gui/group/GroupModel.cpp
+++ b/src/gui/group/GroupModel.cpp
@@ -357,7 +357,7 @@ QMimeData* GroupModel::mimeData(const QModelIndexList& indexes) const
         return nullptr;
     }
     else {
-        data->setData(mimeTypes().first(), encoded);
+        data->setData(mimeTypes().at(0), encoded);
         return data;
     }
 }
diff --git a/src/gui/group/GroupModel.h b/src/gui/group/GroupModel.h
index 95cf1c1cf..0ef0ba990 100644
--- a/src/gui/group/GroupModel.h
+++ b/src/gui/group/GroupModel.h
@@ -33,8 +33,8 @@ public:
     QModelIndex index(Group* group) const;
     Group* groupFromIndex(const QModelIndex& index) const;
 
-    int rowCount(const QModelIndex& parent = QModelIndex()) const;
-    int columnCount(const QModelIndex& parent = QModelIndex()) const;
+    int rowCount(const QModelIndex& parent = QModelIndex()) const override;
+    int columnCount(const QModelIndex& parent = QModelIndex()) const override;
     QModelIndex index(int row, int column, const QModelIndex& parent = QModelIndex()) const override;
     QModelIndex parent(const QModelIndex& index) const override;
     QVariant data(const QModelIndex& index, int role = Qt::DisplayRole) const override;
diff --git a/src/gui/group/GroupView.h b/src/gui/group/GroupView.h
index 69c7ee8ee..e6d2b660c 100644
--- a/src/gui/group/GroupView.h
+++ b/src/gui/group/GroupView.h
@@ -47,7 +47,7 @@ private Q_SLOTS:
     void modelReset();
 
 protected:
-    void dragMoveEvent(QDragMoveEvent* event);
+    void dragMoveEvent(QDragMoveEvent* event) Q_DECL_OVERRIDE;
 
 private:
     void recInitExpanded(Group* group);
diff --git a/src/streams/HashedBlockStream.h b/src/streams/HashedBlockStream.h
index b0d90c9c3..ca4b1fda0 100644
--- a/src/streams/HashedBlockStream.h
+++ b/src/streams/HashedBlockStream.h
@@ -31,8 +31,8 @@ public:
     HashedBlockStream(QIODevice* baseDevice, qint32 blockSize);
     ~HashedBlockStream();
 
-    bool reset();
-    void close();
+    bool reset() Q_DECL_OVERRIDE;
+    void close() Q_DECL_OVERRIDE;
 
 protected:
     qint64 readData(char* data, qint64 maxSize) override;
diff --git a/tests/TestEntry.cpp b/tests/TestEntry.cpp
index 53d68b5e0..1eaca3243 100644
--- a/tests/TestEntry.cpp
+++ b/tests/TestEntry.cpp
@@ -119,6 +119,6 @@ void TestEntry::testClone()
     QCOMPARE(entryCloneNone->uuid(), entryOrg->uuid());
     QCOMPARE(entryCloneHistory->title(), QString("New Title"));
     QCOMPARE(entryCloneHistory->historyItems().size(), 1);
-    QCOMPARE(entryCloneHistory->historyItems().first()->title(), QString("Original Title"));
+    QCOMPARE(entryCloneHistory->historyItems().at(0)->title(), QString("Original Title"));
     QCOMPARE(entryCloneHistory->timeInfo().creationTime(), entryOrg->timeInfo().creationTime());
 }
diff --git a/tests/TestExporter.cpp b/tests/TestExporter.cpp
index 46319bc3e..b205034b1 100644
--- a/tests/TestExporter.cpp
+++ b/tests/TestExporter.cpp
@@ -59,19 +59,19 @@ void TestExporter::testToDbExporter()
     Database* dbExp = ToDbExporter().exportGroup(groupOrg);
 
     QCOMPARE(dbExp->rootGroup()->children().size(), 1);
-    Group* groupExp = dbExp->rootGroup()->children().first();
+    Group* groupExp = dbExp->rootGroup()->children().at(0);
     QVERIFY(groupExp != groupOrg);
     QCOMPARE(groupExp->name(), groupOrg->name());
     QCOMPARE(groupExp->entries().size(), 1);
 
-    Entry* entryExp = groupExp->entries().first();
+    Entry* entryExp = groupExp->entries().at(0);
     QCOMPARE(entryExp->title(), entryOrg->title());
     QCOMPARE(dbExp->metadata()->customIcons().size(), 1);
     QVERIFY(dbExp->metadata()->containsCustomIcon(iconUuid));
     QCOMPARE(entryExp->iconNumber(), entryOrg->iconNumber());
 
     QCOMPARE(entryExp->historyItems().size(), 1);
-    QCOMPARE(entryExp->historyItems().first()->iconUuid(), iconUuid);
+    QCOMPARE(entryExp->historyItems().at(0)->iconUuid(), iconUuid);
 
     delete dbOrg;
     delete dbExp;
diff --git a/tests/TestKeePass1Reader.cpp b/tests/TestKeePass1Reader.cpp
index 14eb5f48c..f60846d26 100644
--- a/tests/TestKeePass1Reader.cpp
+++ b/tests/TestKeePass1Reader.cpp
@@ -70,7 +70,7 @@ void TestKeePass1Reader::testBasic()
     QVERIFY(entry11->timeInfo().expires());
     QCOMPARE(entry11->timeInfo().expiryTime(), genDT(2012, 5, 9, 10, 32));
     QCOMPARE(entry11->attachments()->keys().size(), 1);
-    QCOMPARE(entry11->attachments()->keys().first(), QString("attachment.txt"));
+    QCOMPARE(entry11->attachments()->keys().at(0), QString("attachment.txt"));
     QCOMPARE(entry11->attachments()->value("attachment.txt"), QByteArray("hello world\n"));
 
     Entry* entry12 = group1->entries().at(1);
@@ -117,7 +117,7 @@ void TestKeePass1Reader::testCustomIcons()
 {
     QCOMPARE(m_db->metadata()->customIcons().size(), 1);
 
-    Entry* entry = m_db->rootGroup()->children().at(1)->entries().first();
+    Entry* entry = m_db->rootGroup()->children().at(1)->entries().at(0);
 
     QCOMPARE(entry->icon().width(), 16);
     QCOMPARE(entry->icon().height(), 16);
diff --git a/tests/TestKeePass2XmlReader.cpp b/tests/TestKeePass2XmlReader.cpp
index 0f9676f5d..635137c8c 100644
--- a/tests/TestKeePass2XmlReader.cpp
+++ b/tests/TestKeePass2XmlReader.cpp
@@ -314,7 +314,7 @@ void TestKeePass2XmlReader::testEntry2()
 
 void TestKeePass2XmlReader::testEntryHistory()
 {
-    const Entry* entryMain = m_db->rootGroup()->entries().first();
+    const Entry* entryMain = m_db->rootGroup()->entries().at(0);
     QCOMPARE(entryMain->historyItems().size(), 2);
 
     {