diff --git a/CHANGELOG.md b/CHANGELOG.md
index c8d2e42..16820f4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,8 @@
 * Handle null/undefined/negative values in `CharacterData` interface methods
 * More spec-correctness fixes for `DOMTokenList`
 * Fix `[src=...]` selectors
+* Spec-correctness fixes for `Document#createElement()` and
+  `Document#createElementNS()`
 
 # domino 2.0.3 (12 Jul 2018)
 * Define `blur()`, `focus()` and `forceSpellCheck()` on `HTMLElement` (#125)
diff --git a/lib/Document.js b/lib/Document.js
index 0c627d1..4bd61e5 100644
--- a/lib/Document.js
+++ b/lib/Document.js
@@ -146,35 +146,54 @@ Document.prototype = Object.create(ContainerNode.prototype, {
   }},
 
   createElement: { value: function(localName) {
+    localName = String(localName);
     if (!xml.isValidName(localName)) utils.InvalidCharacterError();
-    if (this.isHTML) localName = utils.toASCIILowerCase(localName);
-    return html.createElement(this, localName, null);
+    // Per spec, namespace should be HTML namespace if "context object is
+    // an HTML document or context object's content type is
+    // "application/xhtml+xml", and null otherwise.
+    // XXX we don't track "context object's content type"
+    if (this.isHTML) {
+      localName = utils.toASCIILowerCase(localName);
+      return html.createElement(this, localName, null);
+    } else {
+      return new Element(this, localName, null, null);
+    }
   }, writable: isApiWritable },
 
   createElementNS: { value: function(namespace, qualifiedName) {
-    if (!xml.isValidName(qualifiedName)) utils.InvalidCharacterError();
-    if (!xml.isValidQName(qualifiedName)) utils.NamespaceError();
-
     var pos, prefix, localName;
-    if ((pos = qualifiedName.indexOf(':')) !== -1) {
+    // Convert parameter types according to WebIDL
+    namespace =
+      (namespace === null || namespace === undefined || namespace === '') ? null :
+      String(namespace);
+    qualifiedName = String(qualifiedName);
+    // See https://github.com/whatwg/dom/issues/671
+    // and https://github.com/whatwg/dom/issues/319
+    if (!xml.isValidQName(qualifiedName)) {
+      utils.InvalidCharacterError();
+    }
+
+    prefix = null;
+    localName = qualifiedName;
+
+    pos = qualifiedName.indexOf(':');
+    if (pos >= 0) {
       prefix = qualifiedName.substring(0, pos);
       localName = qualifiedName.substring(pos+1);
-
-      if (namespace === '' ||
-        (prefix === 'xml' && namespace !== NAMESPACE.XML))
-        utils.NamespaceError();
     }
-    else {
-      prefix = null;
-      localName = qualifiedName;
+    if (prefix !== null && namespace === null) {
+      utils.NamespaceError();
     }
-
-    if (((qualifiedName === 'xmlns' || prefix === 'xmlns') &&
-       namespace !== NAMESPACE.XMLNS) ||
-      (namespace === NAMESPACE.XMLNS &&
-       qualifiedName !== 'xmlns' &&
-       prefix !== 'xmlns'))
+    if (prefix === 'xml' && namespace !== NAMESPACE.XML) {
+      utils.NamespaceError();
+    }
+    if ((prefix === 'xmlns' || qualifiedName === 'xmlns') &&
+        namespace !== NAMESPACE.XMLNS) {
       utils.NamespaceError();
+    }
+    if (namespace === NAMESPACE.XMLNS && !(prefix==='xmlns' || qualifiedName==='xmlns')) {
+      utils.NamespaceError();
+    }
 
     if (namespace === NAMESPACE.HTML) {
       return html.createElement(this, localName, prefix);