diff --git a/Lib/mutex.py b/Lib/mutex.py
index 2348a2e..33baea1 100644
--- a/Lib/mutex.py
+++ b/Lib/mutex.py
@@ -12,6 +12,8 @@
 for lock, where a function is called once the lock is aquired.
 """
 
+__all__ = ["mutex"]
+
 class mutex:
     def __init__(self):
         """Create a new mutex -- initially unlocked."""