diff --git a/lib/morph.js b/lib/morph.js
index ccc20cf..f32eb48 100644
--- a/lib/morph.js
+++ b/lib/morph.js
@@ -47,9 +47,16 @@ function copyAttrs (newNode, oldNode) {
     attrNamespaceURI = attr.namespaceURI
     attrValue = attr.value
     if (attrNamespaceURI) {
-      attrName = attr.localName || attrName
-      fromValue = oldNode.getAttributeNS(attrNamespaceURI, attrName)
+      var attrLocalName = attr.localName
+
+      // Important: getAttributeNS expects the localName of a namespaced attribute
+      // ref: https://dom.spec.whatwg.org/#dom-element-getattributens
+      // ref: https://www.w3.org/TR/DOM-Level-2-Core/glossary.html#dt-localname
+      fromValue = oldNode.getAttributeNS(attrNamespaceURI, attrLocalName || attrName)
       if (fromValue !== attrValue) {
+        // but setAttributeNS requires the fully qualified name
+        // ref: https://dom.spec.whatwg.org/#dom-element-setattributens
+        // ref: https://www.w3.org/TR/DOM-Level-2-Core/glossary.html#dt-qualifiedname
         oldNode.setAttributeNS(attrNamespaceURI, attrName, attrValue)
       }
     } else {