diff -r 8c355edc5b1d Doc/library/os.rst
--- a/Doc/library/os.rst	Sat Dec 17 08:02:20 2011 -0500
+++ b/Doc/library/os.rst	Sat Dec 17 17:10:48 2011 +0100
@@ -977,7 +977,7 @@
    by *how*: :const:`SEEK_SET` or ``0`` to set the position relative to the
    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.
+   the file. Return the new cursor position in bytes, starting from the beginning.
 
    Availability: Unix, Windows.
 
diff -r 8c355edc5b1d Modules/posixmodule.c
--- a/Modules/posixmodule.c	Sat Dec 17 08:02:20 2011 -0500
+++ b/Modules/posixmodule.c	Sat Dec 17 17:10:48 2011 +0100
@@ -6946,7 +6946,8 @@
 
 PyDoc_STRVAR(posix_lseek__doc__,
 "lseek(fd, pos, how) -> newpos\n\n\
-Set the current position of a file descriptor.");
+Set the current position of a file descriptor.\n\
+Return the new cursor position in bytes, starting from the beginning.");
 
 static PyObject *
 posix_lseek(PyObject *self, PyObject *args)