#5458: add a note when we started to raise RuntimeErrors.
diff --git a/Doc/library/threading.rst b/Doc/library/threading.rst
index e6616db..69593ae 100644
--- a/Doc/library/threading.rst
+++ b/Doc/library/threading.rst
@@ -21,8 +21,13 @@
deprecation of the ``camelCase`` names and they remain fully supported in
both Python 2.x and 3.x.
-This module defines the following functions and objects:
+.. note::
+ Starting with Python 2.5, several Thread methods raise :exc:`RuntimeError`
+ instead of :exc:`AssertionError` if called erroneously.
+
+
+This module defines the following functions and objects:
.. function:: active_count()
activeCount()