diff --git a/Lib/threading.py b/Lib/threading.py
index c996f426cda..178c8fd33ca 100644
--- a/Lib/threading.py
+++ b/Lib/threading.py
@@ -450,7 +450,7 @@ def start(self):
             raise RuntimeError("thread.__init__() not called")
 
         if self._started.is_set():
-            raise RuntimeError("thread already started")
+            raise RuntimeError("threads can only be started once")
         if __debug__:
             self._note("%s.start(): starting thread", self)
         with _active_limbo_lock: