Two nits.
diff --git a/Doc/library/constants.rst b/Doc/library/constants.rst
index 634656a..0d44b7b 100644
--- a/Doc/library/constants.rst
+++ b/Doc/library/constants.rst
@@ -8,7 +8,8 @@
 .. note::
 
    :data:`None`, :data:`False`, :data:`True` and :data:`__debug__` cannot be
-   reassigned, so they can be considered "true" constants.
+   reassigned (assignments to them raise :exc:`SyntaxError`), so they can be
+   considered "true" constants.
 
 .. XXX False, True, None are keywords too