diff --git a/dom.bs b/dom.bs
index f1d8d9406..28929e3ca 100644
--- a/dom.bs
+++ b/dom.bs
@@ -6124,6 +6124,8 @@ its <a for=Element>attribute list</a> <a for=list>is empty</a>.
 <a>attribute</a> <var>attribute</var> to <var>value</var>, run these steps:
 
 <ol>
+ <li><p>Assert: <var>attribute</var>'s <a for=Attr>element</a> is non-null.
+
  <li><p><a>Handle attribute changes</a> for <var>attribute</var> with <var>attribute</var>'s
  <a for=Attr>element</a>, <var>attribute</var>'s <a for=Attr>value</a>, and <var>value</var>.
 
@@ -6135,8 +6137,8 @@ its <a for=Element>attribute list</a> <a for=list>is empty</a>.
 steps:
 
 <ol>
- <li><p><a>Handle attribute changes</a> for <var>attribute</var> with <var>element</var>, null, and
- <var>attribute</var>'s <a for=Attr>value</a>.
+ <li><p><a>Handle attribute changes</a> for <var>attribute</var> with <var>element</var>,
+ <var>attribute</var>'s <a for=Attr>value</a>, and <var>value</var>.
 
  <li><p><a for=list>Append</a> <var>attribute</var> to <var>element</var>'s
  <a for=Element>attribute list</a>.
@@ -6148,8 +6150,12 @@ steps:
 <a>attribute</a> <var>attribute</var>, run these steps:
 
 <ol>
- <li><p><a>Handle attribute changes</a> for <var>attribute</var> with <var>attribute</var>'s
- <a for=Attr>element</a>, <var>attribute</var>'s <a for=Attr>value</a>, and null.
+ <li><p>Let <var>element</var> be <var>attribute</var>'s <a for=Attr>element</a>.
+
+ <li><p>Assert: <var>element</var> is non-null.
+
+ <li><p><a>Handle attribute changes</a> for <var>attribute</var> with <var>element</var>,
+ <var>attribute</var>'s <a for=Attr>value</a>, and null.
 
  <li><a for=list>Remove</a> <var>attribute</var> from <var>attribute</var>'s
  <a for=Attr>element</a>'s <a for=Element>attribute list</a>.
@@ -6161,12 +6167,12 @@ steps:
 <a>attribute</a> <var>oldAttr</var> with an <a>attribute</a> <var>newAttr</var>, run these steps:
 
 <ol>
- <li><p><a>Handle attribute changes</a> for <var>oldAttr</var> with <var>oldAttr</var>'s
- <a for=Attr>element</a>, <var>oldAttr</var>'s <a for=Attr>value</a>, and <var>newAttr</var>'s
- <a for=Attr>value</a>.
+ <li><p>Let <var>element</var> be <var>oldAttr</var>'s <a for=Attr>element</a>.
 
- <li><p><a for=list>Replace</a> <var>oldAttr</var> by <var>newAttr</var> in <var>oldAttr</var>'s
- <a for=Attr>element</a>'s <a for=Element>attribute list</a>.
+ <li><p>Assert: <var>element</var> is non-null.
+
+ <li><p><a>Handle attribute changes</a> for <var>oldAttr</var> with <var>element</var>,
+ <var>oldAttr</var>'s <a for=Attr>value</a>, and <var>newAttr</var>'s <a for=Attr>value</a>.
 
  <li><p>Set <var>newAttr</var>'s <a for=Attr>element</a> to <var>oldAttr</var>'s
  <a for=Attr>element</a>.