Issue #18200: Update the stdlib (except tests) to use
ModuleNotFoundError.
diff --git a/Lib/bz2.py b/Lib/bz2.py
index 6e6a2b9..f42045f 100644
--- a/Lib/bz2.py
+++ b/Lib/bz2.py
@@ -14,7 +14,7 @@
 
 try:
     from threading import RLock
-except ImportError:
+except ModuleNotFoundError:
     from dummy_threading import RLock
 
 from _bz2 import BZ2Compressor, BZ2Decompressor