diff --git a/src/CustomElements.js b/src/CustomElements.js
index 8d2cd4a..3f22b0d 100644
--- a/src/CustomElements.js
+++ b/src/CustomElements.js
@@ -321,6 +321,7 @@ if (useNative) {
   // https://dvcs.w3.org/hg/webcomponents/raw-file/tip/spec/custom/
   // index.html#dfn-attribute-changed-callback
   function changeAttribute(name, value, operation) {
+    name = name.toLowerCase();
     var oldValue = this.getAttribute(name);
     operation.apply(this, arguments);
     var newValue = this.getAttribute(name);
diff --git a/test/html/attributes.html b/test/html/attributes.html
index ed79e56..e58eb82 100644
--- a/test/html/attributes.html
+++ b/test/html/attributes.html
@@ -31,7 +31,7 @@
         chai.assert.isFalse(xfoo.removeAttributeOk);
         chai.assert.isFalse(xfoo.setAttributeOk);
         chai.assert.isFalse(xfoo.attributeChangedOk);
-        xfoo.setAttribute('squid', 'tentacles');
+        xfoo.setAttribute('Squid', 'tentacles');
         chai.assert.isTrue(xfoo.setAttributeOk);
         chai.assert.isTrue(xfoo.attributeChangedOk);
         xfoo.attributeChangedOk = false;