diff --git a/docs/hazmat/primitives/padding.rst b/docs/hazmat/primitives/padding.rst
index 475976a..0b76327 100644
--- a/docs/hazmat/primitives/padding.rst
+++ b/docs/hazmat/primitives/padding.rst
@@ -56,6 +56,8 @@
 
 .. class:: ANSIX923(block_size)
 
+    .. versionadded:: 1.3
+
     `ANSI X.923`_ padding works by appending ``N-1`` bytes with the value of
     ``0`` and a last byte with the value of ``chr(N)``, where ``N`` is the
     number of bytes required to make the final block of data the same size as