diff --git a/qt_ui/simcontroller.py b/qt_ui/simcontroller.py
index 33af32cb..fbfb88b5 100644
--- a/qt_ui/simcontroller.py
+++ b/qt_ui/simcontroller.py
@@ -44,6 +44,9 @@ class SimController(QObject):
         self.recreate_game_loop(game)
         self.sim_speed_reset.emit(SimSpeedSetting.PAUSED)
 
+    def shut_down(self) -> None:
+        self._sim_update_thread.stop()
+
     def recreate_game_loop(self, game: Optional[Game]) -> None:
         if self.game_loop is not None:
             self._sim_update_thread.on_sim_pause()
diff --git a/qt_ui/windows/QLiberationWindow.py b/qt_ui/windows/QLiberationWindow.py
index bc9ae7b8..05f5564a 100644
--- a/qt_ui/windows/QLiberationWindow.py
+++ b/qt_ui/windows/QLiberationWindow.py
@@ -389,6 +389,7 @@ class QLiberationWindow(QMainWindow):
             QMessageBox.Yes | QMessageBox.No,
         )
         if result == QMessageBox.Yes:
+            self.sim_controller.shut_down()
             super().closeEvent(event)
             self.dialog = None
         else: