diff --git a/html5lib/constants.py b/html5lib/constants.py
index <HASH>..<HASH> 100644
--- a/html5lib/constants.py
+++ b/html5lib/constants.py
@@ -467,6 +467,7 @@ booleanAttributes = {
     "details": frozenset(("open",)),
     "datagrid": frozenset(("multiple", "disabled")),
     "command": frozenset(("hidden", "disabled", "checked", "default")),
+    "hr": frozenset(("noshade")),
     "menu": frozenset(("autosubmit",)),
     "fieldset": frozenset(("disabled", "readonly")),
     "option": frozenset(("disabled", "readonly", "selected")),
Add @noshade as a boolean attribute. Fixes #<I>. Thanks to fantasai for the patch.