diff --git a/Doc/c-api/set.rst b/Doc/c-api/set.rst
index 3d8cf87..83d9532 100644
--- a/Doc/c-api/set.rst
+++ b/Doc/c-api/set.rst
@@ -50,6 +50,12 @@
 the constructor functions work with any iterable Python object.
 
 
+.. cfunction:: int PySet_Check(PyObject *p)
+
+   Return true if *p* is a :class:`set` object or an instance of a subtype.
+
+   .. versionadded:: 2.6
+
 .. cfunction:: int PyAnySet_Check(PyObject *p)
 
    Return true if *p* is a :class:`set` object, a :class:`frozenset` object, or an
@@ -84,6 +90,11 @@
    set on success or *NULL* on failure.  Raise :exc:`TypeError` if *iterable* is
    not actually iterable.
 
+   .. versionchanged:: 2.6
+      Now guaranteed to return a brand-new :class:`frozenset`.  Formerly,
+      frozensets of zero-length were a singleton.  This got in the way of 
+      building-up new frozensets with :meth:`PySet_Add`.
+
 The following functions and macros are available for instances of :class:`set`
 or :class:`frozenset` or instances of their subtypes.
 
@@ -110,9 +121,6 @@
    the *key* is unhashable. Raise :exc:`PyExc_SystemError` if *anyset* is not a
    :class:`set`, :class:`frozenset`, or an instance of a subtype.
 
-The following functions are available for instances of :class:`set` or its
-subtypes but not for instances of :class:`frozenset` or its subtypes.
-
 
 .. cfunction:: int PySet_Add(PyObject *set, PyObject *key)
 
@@ -122,6 +130,14 @@
    Raise a :exc:`SystemError` if *set* is an not an instance of :class:`set` or its
    subtype.
 
+   .. versionchanged:: 2.6
+      Now works with instances of :class:`frozenset` or its subtypes.
+      Like :cfunc:`PyTuple_SetItem` in that it can be used to fill-in the
+      values of brand new frozensets before they are exposed to other code.
+
+The following functions are available for instances of :class:`set` or its
+subtypes but not for instances of :class:`frozenset` or its subtypes.
+
 
 .. cfunction:: int PySet_Discard(PyObject *set, PyObject *key)