diff --git a/nbformat/sign.py b/nbformat/sign.py
index 90ea140..82c6478 100644
--- a/nbformat/sign.py
+++ b/nbformat/sign.py
@@ -585,7 +585,7 @@ def _config_file_name_default(self):
     jupyter trust mynotebook.ipynb and_this_one.ipynb
     """
 
-    flags = trust_flags
+    flags = trust_flags  # type:ignore[assignment]
 
     reset = Bool(
         False,