diff --git a/src/calibre/gui2/tweak_book/boss.py b/src/calibre/gui2/tweak_book/boss.py
index e00300b8f5..fb689f6bc9 100644
--- a/src/calibre/gui2/tweak_book/boss.py
+++ b/src/calibre/gui2/tweak_book/boss.py
@@ -795,6 +795,8 @@ class Boss(QObject):
 
     @in_thread_job
     def check_requested(self, *args):
+        if current_container() is None:
+            return
         self.commit_all_editors_to_container()
         c = self.gui.check_book
         c.parent().show()