diff --git a/src/duckstation-qt/mainwindow.cpp b/src/duckstation-qt/mainwindow.cpp
index 868184ec8..ac90a8a83 100644
--- a/src/duckstation-qt/mainwindow.cpp
+++ b/src/duckstation-qt/mainwindow.cpp
@@ -33,12 +33,12 @@ MainWindow::~MainWindow()
   Assert(!m_display_widget);
 }
 
-void MainWindow::reportError(QString message)
+void MainWindow::reportError(const QString& message)
 {
   QMessageBox::critical(nullptr, tr("DuckStation Error"), message, QMessageBox::Ok);
 }
 
-void MainWindow::reportMessage(QString message)
+void MainWindow::reportMessage(const QString& message)
 {
   m_ui.statusBar->showMessage(message, 2000);
 }
@@ -129,7 +129,7 @@ void MainWindow::onSystemPerformanceCountersUpdated(float speed, float fps, floa
     QStringLiteral("%1ms average, %2ms worst").arg(average_frame_time, 0, 'f', 2).arg(worst_frame_time, 0, 'f', 2));
 }
 
-void MainWindow::onRunningGameChanged(QString filename, QString game_code, QString game_title)
+void MainWindow::onRunningGameChanged(const QString& filename, const QString& game_code, const QString& game_title)
 {
   m_host_interface->populateSaveStateMenus(game_code.toStdString().c_str(), m_ui.menuLoadState, m_ui.menuSaveState);
   if (game_title.isEmpty())
diff --git a/src/duckstation-qt/mainwindow.h b/src/duckstation-qt/mainwindow.h
index a5edd98fc..600b9c77d 100644
--- a/src/duckstation-qt/mainwindow.h
+++ b/src/duckstation-qt/mainwindow.h
@@ -22,8 +22,8 @@ public:
   ~MainWindow();
 
 private Q_SLOTS:
-  void reportError(QString message);
-  void reportMessage(QString message);
+  void reportError(const QString& message);
+  void reportMessage(const QString& message);
   void createDisplayWindow(QThread* worker_thread, bool use_debug_device);
   void destroyDisplayWindow();
   void toggleFullscreen();
@@ -32,7 +32,7 @@ private Q_SLOTS:
   void onEmulationPaused(bool paused);
   void onSystemPerformanceCountersUpdated(float speed, float fps, float vps, float average_frame_time,
                                           float worst_frame_time);
-  void onRunningGameChanged(QString filename, QString game_code, QString game_title);
+  void onRunningGameChanged(const QString& filename, const QString& game_code, const QString& game_title);
 
   void onStartDiscActionTriggered();
   void onChangeDiscFromFileActionTriggered();
diff --git a/src/duckstation-qt/qthostinterface.cpp b/src/duckstation-qt/qthostinterface.cpp
index 7b787d06b..8200313ea 100644
--- a/src/duckstation-qt/qthostinterface.cpp
+++ b/src/duckstation-qt/qthostinterface.cpp
@@ -167,11 +167,11 @@ QtDisplayWindow* QtHostInterface::createDisplayWindow()
   return m_display_window;
 }
 
-void QtHostInterface::bootSystemFromFile(QString filename)
+void QtHostInterface::bootSystemFromFile(const QString& filename)
 {
   if (!isOnWorkerThread())
   {
-    QMetaObject::invokeMethod(this, "bootSystemFromFile", Qt::QueuedConnection, Q_ARG(QString, filename));
+    QMetaObject::invokeMethod(this, "bootSystemFromFile", Qt::QueuedConnection, Q_ARG(const QString&, filename));
     return;
   }
 
@@ -527,7 +527,7 @@ void QtHostInterface::pauseSystem(bool paused)
   emit emulationPaused(paused);
 }
 
-void QtHostInterface::changeDisc(QString new_disc_filename) {}
+void QtHostInterface::changeDisc(const QString& new_disc_filename) {}
 
 void QtHostInterface::populateSaveStateMenus(const char* game_code, QMenu* load_menu, QMenu* save_menu)
 {
@@ -579,11 +579,11 @@ void QtHostInterface::populateSaveStateMenus(const char* game_code, QMenu* load_
   }
 }
 
-void QtHostInterface::loadState(QString filename)
+void QtHostInterface::loadState(const QString& filename)
 {
   if (!isOnWorkerThread())
   {
-    QMetaObject::invokeMethod(this, "loadState", Qt::QueuedConnection, Q_ARG(QString, filename));
+    QMetaObject::invokeMethod(this, "loadState", Qt::QueuedConnection, Q_ARG(const QString&, filename));
     return;
   }
 
diff --git a/src/duckstation-qt/qthostinterface.h b/src/duckstation-qt/qthostinterface.h
index e0ff40d65..aa672e9eb 100644
--- a/src/duckstation-qt/qthostinterface.h
+++ b/src/duckstation-qt/qthostinterface.h
@@ -61,8 +61,8 @@ public:
   void populateSaveStateMenus(const char* game_code, QMenu* load_menu, QMenu* save_menu);
 
 Q_SIGNALS:
-  void errorReported(QString message);
-  void messageReported(QString message);
+  void errorReported(const QString& message);
+  void messageReported(const QString& message);
   void emulationStarted();
   void emulationStopped();
   void emulationPaused(bool paused);
@@ -72,17 +72,17 @@ Q_SIGNALS:
   void toggleFullscreenRequested();
   void systemPerformanceCountersUpdated(float speed, float fps, float vps, float avg_frame_time,
                                         float worst_frame_time);
-  void runningGameChanged(QString filename, QString game_code, QString game_title);
+  void runningGameChanged(const QString& filename, const QString& game_code, const QString& game_title);
 
 public Q_SLOTS:
   void applySettings();
-  void bootSystemFromFile(QString filename);
+  void bootSystemFromFile(const QString& filename);
   void bootSystemFromBIOS();
   void destroySystem(bool save_resume_state = false, bool block_until_done = false);
   void resetSystem();
   void pauseSystem(bool paused);
-  void changeDisc(QString new_disc_filename);
-  void loadState(QString filename);
+  void changeDisc(const QString& new_disc_filename);
+  void loadState(const QString& filename);
   void loadState(bool global, qint32 slot);
   void saveState(bool global, qint32 slot, bool block_until_done = false);