diff --git a/src/calibre/gui2/tweak_book/completion/worker.py b/src/calibre/gui2/tweak_book/completion/worker.py
index a9d75f6bff..cb8cba21a9 100644
--- a/src/calibre/gui2/tweak_book/completion/worker.py
+++ b/src/calibre/gui2/tweak_book/completion/worker.py
@@ -139,7 +139,7 @@ class CompletionWorker(Thread):
     def shutdown(self):
         self.shutting_down = True
         self.main_queue.put(None)
-        for conn in (self.control_conn, self.data_conn):
+        for conn in (getattr(self, 'control_conn', None), getattr(self, 'data_conn', None)):
             try:
                 conn.close()
             except Exception: