diff --git a/CMakeLists.txt b/CMakeLists.txt
index cde795ad2..04136751f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -198,6 +198,7 @@ if(WITH_TESTS)
 endif(WITH_TESTS)
 
 find_package(Qt5Core          5.2 REQUIRED)
+find_package(Qt5Network       5.2 REQUIRED)
 find_package(Qt5Concurrent    5.2 REQUIRED)
 find_package(Qt5Widgets       5.2 REQUIRED)
 find_package(Qt5Test          5.2 REQUIRED)
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 786a03a80..d0fb3ab51 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -195,6 +195,7 @@ target_link_libraries(keepassx_core
                       ${YUBIKEY_LIBRARIES}
                       zxcvbn
                       Qt5::Core
+                      Qt5::Network
                       Qt5::Concurrent
                       Qt5::Widgets
                       ${GCRYPT_LIBRARIES}
diff --git a/src/gui/Application.cpp b/src/gui/Application.cpp
index f64a766f5..6a7e37057 100644
--- a/src/gui/Application.cpp
+++ b/src/gui/Application.cpp
@@ -22,6 +22,9 @@
 #include <QAbstractNativeEventFilter>
 #include <QFileOpenEvent>
 #include <QSocketNotifier>
+#include <QLockFile>
+#include <QStandardPaths>
+#include <QtNetwork/QLocalSocket>
 
 #include "autotype/AutoType.h"
 
@@ -76,6 +79,8 @@ Application::Application(int& argc, char** argv)
 #ifdef Q_OS_UNIX
     , m_unixSignalNotifier(nullptr)
 #endif
+    , alreadyRunning(false)
+    , lock(nullptr)
 {
 #if defined(Q_OS_UNIX) && !defined(Q_OS_OSX)
     installNativeEventFilter(new XcbEventFilter());
@@ -85,6 +90,58 @@ Application::Application(int& argc, char** argv)
 #if defined(Q_OS_UNIX)
     registerUnixSignals();
 #endif
+
+    QString userName = qgetenv("USER");
+    if (userName.isEmpty()) {
+        userName = qgetenv("USERNAME");
+    }
+    QString identifier = "keepassx2";
+    if (!userName.isEmpty()) {
+        identifier.append("-");
+        identifier.append(userName);
+    }
+    QString socketName = identifier + ".socket";
+    QString lockName = identifier + ".lock";
+
+    // According to documentation we should use RuntimeLocation on *nixes, but even Qt doesn't respect
+    // this and creates sockets in TempLocation, so let's be consistent.
+    lock = new QLockFile(QStandardPaths::writableLocation(QStandardPaths::TempLocation) + "/" + lockName);
+    lock->setStaleLockTime(0);
+    lock->tryLock();
+    switch (lock->error()) {
+    case QLockFile::NoError:
+        server.setSocketOptions(QLocalServer::UserAccessOption);
+        server.listen(socketName);
+        connect(&server, SIGNAL(newConnection()), this, SIGNAL(anotherInstanceStarted()));
+        break;
+    case QLockFile::LockFailedError: {
+        alreadyRunning = true;
+        // notify the other instance
+        // try several times, in case the other instance is still starting up
+        QLocalSocket client;
+        for (int i = 0; i < 3; i++) {
+            client.connectToServer(socketName);
+            if (client.waitForConnected(150)) {
+                client.abort();
+                break;
+            }
+        }
+        break;
+    }
+    default:
+        qWarning() << QCoreApplication::translate("Main",
+                                                  "The lock file could not be created. Single-instance mode disabled.")
+                      .toUtf8().constData();
+    }
+}
+
+Application::~Application()
+{
+    server.close();
+    if (lock) {
+        lock->unlock();
+        delete lock;
+    }
 }
 
 QWidget* Application::mainWindow() const
@@ -171,3 +228,9 @@ void Application::quitBySignal()
         static_cast<MainWindow*>(m_mainWindow)->appExit();
 }
 #endif
+
+bool Application::isAlreadyRunning() const
+{
+    return alreadyRunning;
+}
+
diff --git a/src/gui/Application.h b/src/gui/Application.h
index fd5ad12e0..1a1b0ee86 100644
--- a/src/gui/Application.h
+++ b/src/gui/Application.h
@@ -20,6 +20,8 @@
 #define KEEPASSX_APPLICATION_H
 
 #include <QApplication>
+#include <QtNetwork/QLocalServer>
+class QLockFile;
 
 class QSocketNotifier;
 
@@ -30,12 +32,15 @@ class Application : public QApplication
 public:
     Application(int& argc, char** argv);
     QWidget* mainWindow() const;
+    ~Application();
     void setMainWindow(QWidget* mainWindow);
 
     bool event(QEvent* event) override;
+    bool isAlreadyRunning() const;
 
 signals:
     void openFile(const QString& filename);
+    void anotherInstanceStarted();
 
 private slots:
 #if defined(Q_OS_UNIX)
@@ -54,6 +59,9 @@ private:
     static void handleUnixSignal(int sig);
     static int unixSignalSocket[2];
 #endif
+    bool alreadyRunning;
+    QLockFile* lock;
+    QLocalServer server;
 };
 
 #endif // KEEPASSX_APPLICATION_H
diff --git a/src/main.cpp b/src/main.cpp
index 5981999e7..a4416e0a9 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -56,6 +56,11 @@ int main(int argc, char** argv)
     // don't set organizationName as that changes the return value of
     // QStandardPaths::writableLocation(QDesktopServices::DataLocation)
 
+    if (app.isAlreadyRunning()) {
+        qWarning() << QCoreApplication::translate("Main", "Another instance of KeePassX 2 is already running.").toUtf8().constData();
+        return 0;
+    }
+
     QApplication::setQuitOnLastWindowClosed(false);
 
     if (!Crypto::init()) {
@@ -102,7 +107,15 @@ int main(int argc, char** argv)
 
     MainWindow mainWindow;
     app.setMainWindow(&mainWindow);
-    
+
+    QObject::connect(&app, &Application::anotherInstanceStarted,
+                    [&]() {
+                        mainWindow.ensurePolished();
+                        mainWindow.setWindowState(mainWindow.windowState() & ~Qt::WindowMinimized);
+                        mainWindow.show();
+                        mainWindow.raise();
+                        mainWindow.activateWindow();
+                    });
     QObject::connect(&app, SIGNAL(openFile(QString)), &mainWindow, SLOT(openDatabase(QString)));
     
     // start minimized if configured