diff --git a/Doc/c-api/intro.rst b/Doc/c-api/intro.rst
@@ -106,6 +106,8 @@ complete listing.
   all possible values are covered in ``case`` statements.  Use this in places
   where you might be tempted to put an ``assert(0)`` or ``abort()`` call.

.. c:macro:: Py_ABS(x)

   Return the absolute value of ``x``.