Issue #18200: Update the stdlib (except tests) to use
ModuleNotFoundError.
diff --git a/Lib/mailbox.py b/Lib/mailbox.py
index 2049516..a45b3bf 100644
--- a/Lib/mailbox.py
+++ b/Lib/mailbox.py
@@ -23,7 +23,7 @@
 import contextlib
 try:
     import fcntl
-except ImportError:
+except ModuleNotFoundError:
     fcntl = None
 
 __all__ = [ 'Mailbox', 'Maildir', 'mbox', 'MH', 'Babyl', 'MMDF',