diff --git a/CHANGES.rst b/CHANGES.rst
index cf95ea0b..47dcda3a 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -11,10 +11,15 @@ Features:
 * Add support for the ``<wbr>`` element in the sanitizer, `which indicates
   a line break opportunity <https://html.spec.whatwg.org/#the-wbr-element>`_.
   This element is allowed by default. (#395) (Thank you, Tom Most!)
+* Add support for serializing the ``<ol reversed>`` boolean attribute. (Thank
+  you, Tom Most!) (#396)
+* The ``<ol reversed>`` and ``<ol start>`` attributes are now permitted by the
+  sanitizer. (#321) (Thank you, Tom Most!)
 
 Bug fixes:
 
-* The sanitizer now permits ``<summary>`` tags.
+* The sanitizer now permits ``<summary>`` tags. It used to allow ``<details>``
+  already. (#423)
 
 1.1
 ~~~
diff --git a/html5lib/constants.py b/html5lib/constants.py
index e83bfb5d..2fa4146d 100644
--- a/html5lib/constants.py
+++ b/html5lib/constants.py
@@ -617,6 +617,7 @@
     "button": frozenset(["disabled", "autofocus"]),
     "input": frozenset(["disabled", "readonly", "required", "autofocus", "checked", "ismap"]),
     "select": frozenset(["disabled", "readonly", "autofocus", "multiple"]),
+    "ol": frozenset(["reversed"]),
     "output": frozenset(["disabled", "readonly"]),
     "iframe": frozenset(["seamless"]),
 }
diff --git a/html5lib/filters/sanitizer.py b/html5lib/filters/sanitizer.py
index f7ac8d9b..81c85d44 100644
--- a/html5lib/filters/sanitizer.py
+++ b/html5lib/filters/sanitizer.py
@@ -365,6 +365,7 @@
     (None, 'maxsize'),
     (None, 'minsize'),
     (None, 'other'),
+    (None, 'reversed'),
     (None, 'rowalign'),
     (None, 'rowalign'),
     (None, 'rowalign'),
@@ -375,6 +376,7 @@
     (None, 'scriptlevel'),
     (None, 'selection'),
     (None, 'separator'),
+    (None, 'start'),
     (None, 'stretchy'),
     (None, 'width'),
     (None, 'width'),
diff --git a/html5lib/tests/test_sanitizer.py b/html5lib/tests/test_sanitizer.py
index a6cbd798..499310b6 100644
--- a/html5lib/tests/test_sanitizer.py
+++ b/html5lib/tests/test_sanitizer.py
@@ -154,3 +154,21 @@ def test_uppercase_color_codes_in_style():
     sanitized = sanitize_html("<p style=\"border: 1px solid #A2A2A2;\"></p>")
     expected = '<p style=\"border: 1px solid #A2A2A2;\"></p>'
     assert expected == sanitized
+
+
+def test_ol_start_allowed():
+    sanitized = sanitize_html("<ol start=2><li>.</ol>")
+    expected = '<ol start="2"><li>.</li></ol>'
+    assert expected == sanitized
+
+
+def test_ol_type_allowed():
+    sanitized = sanitize_html("<ol type=I><li>.</ol>")
+    expected = '<ol type="I"><li>.</li></ol>'
+    assert expected == sanitized
+
+
+def test_ol_reversed_allowed():
+    sanitized = sanitize_html("<ol reversed><li>.</ol>")
+    expected = '<ol reversed><li>.</li></ol>'
+    assert expected == sanitized