diff --git a/Doc/library/_thread.rst b/Doc/library/_thread.rst
index 369e9cd..e7e7504 100644
--- a/Doc/library/_thread.rst
+++ b/Doc/library/_thread.rst
@@ -35,6 +35,9 @@
 
    Raised on thread-specific errors.
 
+   .. versionchanged:: 3.3
+      This is now a synonym of the built-in :exc:`RuntimeError`.
+
 
 .. data:: LockType