diff --git a/Doc/library/ast.rst b/Doc/library/ast.rst
--- a/Doc/library/ast.rst
+++ b/Doc/library/ast.rst
@@ -244,3 +244,11 @@ and classes for traversing abstract synt
    wanted *annotate_fields* must be set to False.  Attributes such as line
    numbers and column offsets are not dumped by default.  If this is wanted,
    *include_attributes* can be set to ``True``.
+
+
+The :mod:`ast` module defines one constant:
+
+.. data:: PyCF_ONLY_AST
+
+  Constant exposed for use with :func:`compile` (see example use in
+  :func:`parse`).