diff --git a/Doc/library/os.rst b/Doc/library/os.rst
index f3e7b5d94ac..2c14f8f485c 100644
--- a/Doc/library/os.rst
+++ b/Doc/library/os.rst
@@ -1056,10 +1056,10 @@ or `the MSDN <http://msdn.microsoft.com/en-us/library/z0kc8e3z.aspx>`_ on Window
    .. versionadded:: 3.3
 
 
-.. function:: pwrite(fd, string, offset)
+.. function:: pwrite(fd, str, offset)
 
-   Write *string* to a file descriptor, *fd*, from *offset*, leaving the file
-   offset unchanged.
+   Write *bytestring* to a file descriptor, *fd*, from *offset*,
+   leaving the file offset unchanged.
 
    Availability: Unix.