diff --git a/gui/qt/util.py b/gui/qt/util.py
index 3312afb7f..e730daed0 100644
--- a/gui/qt/util.py
+++ b/gui/qt/util.py
@@ -229,12 +229,12 @@ class WaitingDialog(WindowModalDialog):
         if isinstance(parent, MessageBoxMixin):
             parent = parent.top_level_window()
         WindowModalDialog.__init__(self, parent, _("Please wait"))
-        self.setAttribute(Qt.WA_DeleteOnClose)  # see #3956
         vbox = QVBoxLayout(self)
         vbox.addWidget(QLabel(message))
         self.accepted.connect(self.on_accepted)
         self.show()
         self.thread = TaskThread(self)
+        self.thread.finished.connect(self.deleteLater)  # see #3956
         self.thread.add(task, on_success, self.accept, on_error)
 
     def wait(self):
@@ -624,12 +624,12 @@ class TaskThread(QThread):
             except BaseException:
                 self.doneSig.emit(sys.exc_info(), task.cb_done, task.cb_error)
 
-    def on_done(self, result, cb_done, cb):
+    def on_done(self, result, cb_done, cb_result):
         # This runs in the parent's thread.
         if cb_done:
             cb_done()
-        if cb:
-            cb(result)
+        if cb_result:
+            cb_result(result)
 
     def stop(self):
         self.tasks.put(None)