builtin -> built-in.
diff --git a/Doc/library/io.rst b/Doc/library/io.rst
index 184e443..3dba0b5 100644
--- a/Doc/library/io.rst
+++ b/Doc/library/io.rst
@@ -10,7 +10,7 @@
.. versionadded:: 2.6
The :mod:`io` module provides the Python interfaces to stream handling. The
-builtin :func:`open` function is defined in this module.
+built-in :func:`open` function is defined in this module.
At the top of the I/O hierarchy is the abstract base class :class:`IOBase`. It
defines the basic interface to a stream. Note, however, that there is no