diff -r 2c9e07db0ac4 Lib/threading.py
--- a/Lib/threading.py	Tue Sep 13 09:27:07 2016 -0700
+++ b/Lib/threading.py	Tue Sep 13 20:42:53 2016 +0200
@@ -838,9 +838,9 @@
         if not self._initialized:
             raise RuntimeError("thread.__init__() not called")
 
-        if self._started.is_set():
-            raise RuntimeError("threads can only be started once")
         with _active_limbo_lock:
+            if self._started.is_set() or self in _limbo:
+                raise RuntimeError("threads can only be started once")
             _limbo[self] = self
         try:
             _start_new_thread(self._bootstrap, ())