diff --git a/packages/dom-helper/lib/main.js b/packages/dom-helper/lib/main.js
index 184d56e1..f891f527 100644
--- a/packages/dom-helper/lib/main.js
+++ b/packages/dom-helper/lib/main.js
@@ -47,16 +47,16 @@ var canClone = doc && (function(document){
 
 // This is not the namespace of the element, but of
 // the elements inside that elements.
-function interiorNamespace(element){
+function interiorNamespace(element) {
   if (
     element &&
     element.namespaceURI === svgNamespace &&
     !svgHTMLIntegrationPoints[element.tagName]
   ) {
     return svgNamespace;
-  } else {
-    return null;
   }
+
+  return null;
 }
 
 // The HTML spec allows for "omitted start tags". These tags are optional
@@ -351,19 +351,18 @@ if (doc && doc.createElementNS) {
   // Only opt into namespace detection if a contextualElement
   // is passed.
   prototype.createElement = function(tagName, contextualElement) {
-    var namespace = this.namespace;
+    let namespace = this.namespace;
     if (contextualElement) {
       if (tagName === 'svg') {
         namespace = svgNamespace;
       } else {
-        namespace = interiorNamespace(contextualElement);
+        namespace = typeof contextualElement === 'string' ? contextualElement : interiorNamespace(contextualElement);
       }
     }
     if (namespace) {
       return this.document.createElementNS(namespace, tagName);
-    } else {
-      return this.document.createElement(tagName);
     }
+    return this.document.createElement(tagName);
   };
   prototype.setAttributeNS = function(element, namespace, name, value) {
     element.setAttributeNS(namespace, name, String(value));
diff --git a/packages/htmlbars-compiler/lib/fragment-javascript-compiler.js b/packages/htmlbars-compiler/lib/fragment-javascript-compiler.js
index e51df292..294790b1 100644
--- a/packages/htmlbars-compiler/lib/fragment-javascript-compiler.js
+++ b/packages/htmlbars-compiler/lib/fragment-javascript-compiler.js
@@ -32,13 +32,21 @@ FragmentJavaScriptCompiler.prototype.createFragment = function() {
   this.source.push(this.indent+'  var '+el+' = dom.createDocumentFragment();\n');
 };
 
-FragmentJavaScriptCompiler.prototype.createElement = function(tagName) {
-  var el = 'el'+(++this.depth);
+FragmentJavaScriptCompiler.prototype.createElement = function(tagName, contextualElement) {
+  let el = 'el'+(++this.depth);
   if (tagName === 'svg') {
     this.pushNamespaceFrame({namespace: svgNamespace, depth: this.depth});
   }
   this.ensureNamespace();
-  this.source.push(this.indent+'  var '+el+' = dom.createElement('+string(tagName)+');\n');
+
+  let toPush = this.indent+'  var '+el+' = dom.createElement('+string(tagName);
+  if (contextualElement) {
+    toPush += ', ' + string(contextualElement);
+  }
+  toPush += ');\n';
+
+  this.source.push(toPush);
+
   if (svgHTMLIntegrationPoints[tagName]) {
     this.pushNamespaceFrame({namespace: null, depth: this.depth});
   }
@@ -60,12 +68,11 @@ FragmentJavaScriptCompiler.prototype.returnNode = function() {
 };
 
 FragmentJavaScriptCompiler.prototype.setAttribute = function(name, value, namespace) {
-  var el = 'el'+this.depth;
+  let el = 'el'+this.depth;
   if (namespace) {
-    this.source.push(this.indent+'  dom.setAttributeNS('+el+','+string(namespace)+','+string(name)+','+string(value)+');\n');
-  } else {
-    this.source.push(this.indent+'  dom.setAttribute('+el+','+string(name)+','+string(value)+');\n');
+    return this.source.push(this.indent+'  dom.setAttributeNS('+el+','+string(namespace)+','+string(name)+','+string(value)+');\n');
   }
+  this.source.push(this.indent+'  dom.setAttribute('+el+','+string(name)+','+string(value)+');\n');
 };
 
 FragmentJavaScriptCompiler.prototype.appendChild = function() {
diff --git a/packages/htmlbars-compiler/lib/fragment-opcode-compiler.js b/packages/htmlbars-compiler/lib/fragment-opcode-compiler.js
index a1d867f5..461b6507 100644
--- a/packages/htmlbars-compiler/lib/fragment-opcode-compiler.js
+++ b/packages/htmlbars-compiler/lib/fragment-opcode-compiler.js
@@ -33,7 +33,17 @@ FragmentOpcodeCompiler.prototype.comment = function(comment) {
 };
 
 FragmentOpcodeCompiler.prototype.openElement = function(element) {
-  this.opcode('createElement', [element.tag]);
+  let contextualElement;
+
+  for (let i = 0; i < element.attributes.length; i++) {
+    let attr = element.attributes[i];
+    if (attr.name === 'is') {
+      contextualElement = attr.value.chars;
+      break;
+    }
+  }
+
+  this.opcode('createElement', [element.tag, contextualElement]);
   forEach(element.attributes, this.attribute, this);
 };
 
diff --git a/packages/htmlbars-compiler/tests/fragment-javascript-compiler-test.js b/packages/htmlbars-compiler/tests/fragment-javascript-compiler-test.js
new file mode 100644
index 00000000..a3919f2f
--- /dev/null
+++ b/packages/htmlbars-compiler/tests/fragment-javascript-compiler-test.js
@@ -0,0 +1,38 @@
+import FragmentJavaScriptCompiler from "../htmlbars-compiler/fragment-javascript-compiler";
+
+QUnit.module('FragmentJavaScriptCompiler');
+
+test('createElement correctly generates code for tagName with contextualElement', assert => {
+  assert.expect(1);
+  let fragmentCompiler = new FragmentJavaScriptCompiler();
+  fragmentCompiler.source.length = 0;
+  fragmentCompiler.depth = -1;
+  fragmentCompiler.indent = "";
+  fragmentCompiler.namespaceFrameStack = [{namespace: null, depth: null}];
+
+  const tagName = 'button';
+  const contextualElement = 'my-button';
+
+  fragmentCompiler.createElement(tagName, contextualElement);
+
+  const pattern = new RegExp(`dom\\.createElement\\("${tagName}", "${contextualElement}"\\)`);
+
+  assert.equal(pattern.test(fragmentCompiler.source[1]), true);
+});
+
+test('createElement correctly generates code for tagName without contextualElement', assert => {
+  assert.expect(1);
+  let fragmentCompiler = new FragmentJavaScriptCompiler();
+  fragmentCompiler.source.length = 0;
+  fragmentCompiler.depth = -1;
+  fragmentCompiler.indent = "";
+  fragmentCompiler.namespaceFrameStack = [{namespace: null, depth: null}];
+
+  const tagName = 'button';
+
+  fragmentCompiler.createElement(tagName);
+
+  const pattern = new RegExp(`dom\\.createElement\\("${tagName}"\\)`);
+
+  assert.equal(pattern.test(fragmentCompiler.source[1]), true);
+});
diff --git a/packages/htmlbars-compiler/tests/fragment-opcode-compiler-test.js b/packages/htmlbars-compiler/tests/fragment-opcode-compiler-test.js
new file mode 100644
index 00000000..ec678f12
--- /dev/null
+++ b/packages/htmlbars-compiler/tests/fragment-opcode-compiler-test.js
@@ -0,0 +1,32 @@
+import FragmentOpcodeCompiler from "../htmlbars-compiler/fragment-opcode-compiler";
+
+QUnit.module('FragmentOpcodeCompiler');
+
+test('openElement calls opcode with correct arguments when element has `is` attribute', assert => {
+  assert.expect(2);
+  let opcodeCompiler = new FragmentOpcodeCompiler();
+
+  const tagName = 'button';
+  const typeExtension = 'my-button';
+  const attributeName = 'is';
+
+  const element = {
+    tag: tagName,
+    attributes: [
+      {
+        name: attributeName,
+        value: {
+          chars: typeExtension
+        }
+      }
+    ]
+  };
+
+  // monkey patch
+  opcodeCompiler.opcode = (opname, args) => {
+    assert.equal(opname, 'createElement');
+    assert.deepEqual(args, [ tagName, typeExtension ]);
+  };
+
+  opcodeCompiler.openElement(element);
+});
diff --git a/packages/htmlbars-compiler/tests/html-compiler-test.js b/packages/htmlbars-compiler/tests/html-compiler-test.js
index 6e6074a5..5f143cd0 100644
--- a/packages/htmlbars-compiler/tests/html-compiler-test.js
+++ b/packages/htmlbars-compiler/tests/html-compiler-test.js
@@ -719,6 +719,22 @@ test("Simple elements can have dashed attributes", function() {
   equalTokens(fragment, '<div aria-label="foo">content</div>');
 });
 
+test("<button is=\"my-button\"> should generate a createElement('button', 'my-button') call", assert => {
+  assert.expect(2);
+
+  const extensionName = 'my-button';
+  const tagName = 'button';
+  const template = compile(`<${tagName} is="${extensionName}"></${tagName}>`);
+
+  let fragment = template.render({ isTrue: true }, env);
+  assert.equal( fragment.fragment.childNodes[0].namespaceURI, extensionName,
+          'button has namespace matching extension name');
+
+  const pattern = new RegExp(`dom\\.createElement\\("${tagName}", "${extensionName}"\\)`);
+
+  assert.equal(pattern.test(fragment.template.buildFragment), true);
+});
+
 QUnit.skip("Block params", function() {
   registerHelper('a', function() {
     this.yieldIn(compile("A({{yield 'W' 'X1'}})"));