Index: os.rst
===================================================================
--- os.rst	(revision 63058)
+++ os.rst	(working copy)
@@ -499,6 +499,8 @@
 
    Return a duplicate of file descriptor *fd*. Availability: Macintosh, Unix,
    Windows.
+   *fd* can either be an integer, or an object with a fileno() method which
+   returns the actual file descriptor
 
 
 .. function:: dup2(fd, fd2)
@@ -520,6 +522,8 @@
    Change the owner and group id of the file given by *fd* to the numeric *uid*
    and *gid*.  To leave one of the ids unchanged, set it to -1.
    Availability: Unix.
+   *fd* can either be an integer, or an object with a fileno() method which
+   returns the actual file descriptor
 
    .. versionadded:: 2.6
 
@@ -546,17 +550,24 @@
    included in ``pathconf_names``, an :exc:`OSError` is raised with
    :const:`errno.EINVAL` for the error number.
 
+   *fd* can either be an integer, or an object with a fileno() method which
+   returns the actual file descriptor
 
+
 .. function:: fstat(fd)
 
    Return status for file descriptor *fd*, like :func:`stat`. Availability:
    Macintosh, Unix, Windows.
+   *fd* can either be an integer, or an object with a fileno() method which
+   returns the actual file descriptor
 
 
 .. function:: fstatvfs(fd)
 
    Return information about the filesystem containing the file associated with file
    descriptor *fd*, like :func:`statvfs`. Availability: Unix.
+   *fd* can either be an integer, or an object with a fileno() method which
+   returns the actual file descriptor
 
 
 .. function:: fsync(fd)
@@ -589,8 +600,9 @@
    beginning of the file; :const:`SEEK_CUR` or ``1`` to set it relative to the
    current position; :const:`os.SEEK_END` or ``2`` to set it relative to the end of
    the file. Availability: Macintosh, Unix, Windows.
+   *fd* can either be an integer, or an object with a fileno() method which
+   returns the actual file descriptor
 
-
 .. function:: open(file, flags[, mode])
 
    Open the file *file* and set various flags according to *flags* and possibly its