diff --git a/Lib/threading.py b/Lib/threading.py
index c485524..2e6fab9 100644
--- a/Lib/threading.py
+++ b/Lib/threading.py
@@ -493,8 +493,40 @@
         self.__block.release()
 
     def __delete(self):
+        """Remove the current thread from the dict of currently running
+        threads.
+
+        Must take care to not raise an exception if dummy_thread is being used
+        (and thus this module is being used as an instance of dummy_threading).
+        Since dummy_thread.get_ident() always returns -1 since there is only one
+        thread if dummy_thread is being used.  This means that if any Thread
+        instances are created they will overwrite any other threads registered.
+
+        This is an issue with this method, though, since an instance of
+        _MainThread is always created by 'threading'.  This gets overwritten the
+        instant an instance of Thread is created; both threads will have -1 as
+        their value from dummy_thread.get_ident() and thus have the same key in
+        the dict.  This means that when the _MainThread instance created by
+        'threading' tries to clean itself up when atexit calls this method it
+        gets a key error if another Thread instance was created since that
+        removed the only thing with the key of -1.
+
+        This all means that KeyError from trying to delete something from
+        _active if dummy_threading is being used is a red herring.  But since
+        it isn't if dummy_threading is *not* being used then don't hide the
+        exception.  Also don't need to worry about issues from interpreter
+        shutdown and sys not being defined because the call is protected by a
+        blanket try/except block where that could be a problem.
+
+        """
         _active_limbo_lock.acquire()
-        del _active[_get_ident()]
+        if _sys.modules.has_key('dummy_threading'):
+            try:
+                del _active[_get_ident()]
+            except KeyError:
+                pass
+        else:
+            del _active[_get_ident()]
         _active_limbo_lock.release()
 
     def join(self, timeout=None):