builtin -> built-in.
diff --git a/Doc/library/sets.rst b/Doc/library/sets.rst
index 6d974d6..47b2d76 100644
--- a/Doc/library/sets.rst
+++ b/Doc/library/sets.rst
@@ -184,7 +184,7 @@
Also note, the module also includes a :meth:`union_update` method which is an
alias for :meth:`update`. The method is included for backwards compatibility.
Programmers should prefer the :meth:`update` method because it is supported by
-the builtin :class:`set()` and :class:`frozenset()` types.
+the built-in :class:`set()` and :class:`frozenset()` types.
.. _set-example: