1 files changed, 4 insertions, 2 deletions
diff --git a/sphinx/errors.py b/sphinx/errors.py
index a0263c613..8521010ff 100644
--- a/sphinx/errors.py
+++ b/sphinx/errors.py
@@ -1,6 +1,6 @@
 """Contains SphinxError and a few subclasses."""
 
-from typing import Any
+from typing import Any, Optional
 
 
 class SphinxError(Exception):
@@ -39,7 +39,9 @@ class ApplicationError(SphinxError):
 class ExtensionError(SphinxError):
     """Extension error."""
 
-    def __init__(self, message: str, orig_exc: Exception = None, modname: str = None) -> None:
+    def __init__(
+        self, message: str, orig_exc: Optional[Exception] = None, modname: Optional[str] = None
+    ) -> None:
         super().__init__(message)
         self.message = message
         self.orig_exc = orig_exc