diff --git a/Doc/library/csv.rst b/Doc/library/csv.rst
index 98fc6c9..1be909b 100644
--- a/Doc/library/csv.rst
+++ b/Doc/library/csv.rst
@@ -127,6 +127,11 @@
    Return the dialect associated with *name*.  An :exc:`Error` is raised if *name*
    is not a registered dialect name.
 
+   .. versionchanged:: 2.5
+
+   This function now returns an immutable :class:`Dialect`.  Previously an
+   instance of the requested dialect was returned.  Users could modify the
+   underlying class, changing the behavior of active readers and writers.
 
 .. function:: list_dialects()