diff --git a/components/script/dom/element.rs b/components/script/dom/element.rs
index 6aeef3ce986..eab06c5c19d 100644
--- a/components/script/dom/element.rs
+++ b/components/script/dom/element.rs
@@ -1674,6 +1674,15 @@ impl ElementMethods for Element {
             }
 
             // Step 4.
+            if self.get_custom_element_definition().is_some() {
+                let old_name = old_attr.local_name().clone();
+                let old_value = DOMString::from(&**old_attr.value());
+                let new_value = DOMString::from(&**attr.value());
+                let namespace = old_attr.namespace().clone();
+                let reaction = CallbackReaction::AttributeChanged(old_name, Some(old_value),
+                    Some(new_value), namespace);
+                ScriptThread::enqueue_callback_reaction(self, reaction, None);
+            }
             self.will_mutate_attr(attr);
             attr.set_owner(Some(self));
             self.attrs.borrow_mut()[position] = JS::from_ref(attr);
diff --git a/tests/wpt/metadata/custom-elements/reactions/Element.html.ini b/tests/wpt/metadata/custom-elements/reactions/Element.html.ini
index 8661d431874..6efc95e4d19 100644
--- a/tests/wpt/metadata/custom-elements/reactions/Element.html.ini
+++ b/tests/wpt/metadata/custom-elements/reactions/Element.html.ini
@@ -6,12 +6,6 @@
   [slot on Element must enqueue an attributeChanged reaction when replacing an existing attribute]
     expected: FAIL
 
-  [setAttributeNode on Element must enqueue an attributeChanged reaction when replacing an existing attribute]
-    expected: FAIL
-
-  [setAttributeNodeNS on Element must enqueue an attributeChanged reaction when replacing an existing attribute]
-    expected: FAIL
-
   [insertAdjacentHTML on Element must enqueue a connected reaction for a newly constructed custom element]
     expected: FAIL
 
diff --git a/tests/wpt/metadata/custom-elements/reactions/NamedNodeMap.html.ini b/tests/wpt/metadata/custom-elements/reactions/NamedNodeMap.html.ini
deleted file mode 100644
index f1dfcdc502e..00000000000
--- a/tests/wpt/metadata/custom-elements/reactions/NamedNodeMap.html.ini
+++ /dev/null
@@ -1,8 +0,0 @@
-[NamedNodeMap.html]
-  type: testharness
-  [setNamedItem on NamedNodeMap must enqueue an attributeChanged reaction when replacing an existing attribute]
-    expected: FAIL
-
-  [setNamedItemNS on NamedNodeMap must enqueue an attributeChanged reaction when replacing an existing attribute]
-    expected: FAIL
-
diff --git a/tests/wpt/mozilla/meta/css/get-computed-style-for-url.html.ini b/tests/wpt/mozilla/meta/css/get-computed-style-for-url.html.ini
index 3f3945a8eb3..4b9fd22e1df 100644
--- a/tests/wpt/mozilla/meta/css/get-computed-style-for-url.html.ini
+++ b/tests/wpt/mozilla/meta/css/get-computed-style-for-url.html.ini
@@ -1,6 +1,5 @@
 [get-computed-style-for-url.html]
   type: testharness
-
   [getComputedStyle(elem) for url() listStyle uses the resolved URL and elem.style uses the original URL]
     expected: FAIL
     bug: https://github.com/servo/servo/issues/18015