diff --git a/Lib/threading.py b/Lib/threading.py
index 2f6ac70..813dae2 100644
--- a/Lib/threading.py
+++ b/Lib/threading.py
@@ -1421,7 +1421,15 @@
 
     # fork() only copied the current thread; clear references to others.
     new_active = {}
-    current = current_thread()
+
+    try:
+        current = _active[get_ident()]
+    except KeyError:
+        # fork() was called in a thread which was not spawned
+        # by threading.Thread. For example, a thread spawned
+        # by thread.start_new_thread().
+        current = _MainThread()
+
     _main_thread = current
 
     # reset _shutdown() locks: threads re-register their _tstate_lock below