diff --git a/pytec/tec_qt.py b/pytec/tec_qt.py
index 7c34377..c2e54d0 100644
--- a/pytec/tec_qt.py
+++ b/pytec/tec_qt.py
@@ -57,6 +57,7 @@ class ClientWatcher(QObject):
     @pyqtSlot()
     def stop_watching(self):
         self.running = False
+        self.watch_task.cancel()
 
     @pyqtSlot()
     def set_update_s(self, update_s):