diff --git a/src/CustomElements/v1/CustomElements.js b/src/CustomElements/v1/CustomElements.js
index 8c97199..65c96a4 100644
--- a/src/CustomElements/v1/CustomElements.js
+++ b/src/CustomElements/v1/CustomElements.js
@@ -143,9 +143,8 @@
       this._definitions.set(localName, definition);
 
       // 5.1.22
-      // The spec says we should upgrade all existing elements now, but if we
-      // defer we can do less tree walks
-      // scheduleUpgrade();
+      // this causes an upgrade of the document
+      this._addNodes(document.childNodes);
     },
 
     flush() {
diff --git a/tests/CustomElements/v1/js/upgrade.js b/tests/CustomElements/v1/js/upgrade.js
new file mode 100644
index 0000000..47bfdd4
--- /dev/null
+++ b/tests/CustomElements/v1/js/upgrade.js
@@ -0,0 +1,124 @@
+/**
+ * @license
+ * Copyright (c) 2014 The Polymer Project Authors. All rights reserved.
+ * This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
+ * The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
+ * The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
+ * Code distributed by Google as part of the polymer project is also
+ * subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
+ */
+
+suite('upgrade', function() {
+  var work;
+  var assert = chai.assert;
+
+  setup(function() {
+    work = document.createElement('div');
+    document.body.appendChild(work);
+  });
+
+  teardown(function() {
+    document.body.removeChild(work);
+  });
+
+  function registerTestComponent(inName, inValue) {
+    var C = class extends HTMLElement {
+      constructor() {
+        customElements.setCurrentTag('inName');
+        super();
+      }
+    };
+    C.prototype.value = inValue || 'value';
+    customElements.define(inName, C);
+  }
+
+  function testElements(node, selector, value) {
+    Array.prototype.forEach.call(node.querySelectorAll(selector), function(n) {
+      assert.equal(n.value, value);
+    });
+  }
+
+  test('custom element automatically upgrades', function(done) {
+    work.innerHTML = '<x-auto></x-auto>';
+    var x = work.firstChild;
+    // must flush after mutations to avoid false passes
+    customElements.flush();
+    assert.isUndefined(x.value);
+    registerTestComponent('x-auto', 'auto');
+    assert.equal(x.value, 'auto');
+    done();
+  });
+
+  test('custom element automatically upgrades in subtree', function(done) {
+    work.innerHTML = '<div></div>';
+    var target = work.firstChild;
+    target.innerHTML = '<x-auto-sub></x-auto-sub>';
+    var x = target.firstChild;
+    // must flush after mutations to avoid false passes
+    customElements.flush();
+    assert.isUndefined(x.value);
+    registerTestComponent('x-auto-sub', 'auto-sub');
+    assert.equal(x.value, 'auto-sub');
+    done();
+  });
+
+  test('custom elements automatically upgrade', function(done) {
+    registerTestComponent('x-auto1', 'auto1');
+    registerTestComponent('x-auto2', 'auto2');
+    work.innerHTML = '<div><div><x-auto1></x-auto1><x-auto1></x-auto1>' +
+      '</div></div><div><x-auto2><x-auto1></x-auto1></x-auto2>' +
+      '<x-auto2><x-auto1></x-auto1></x-auto2></div>';
+    customElements.flush();
+    testElements(work, 'x-auto1', 'auto1');
+    testElements(work, 'x-auto2', 'auto2');
+    done();
+  });
+
+  test('custom elements automatically upgrade in subtree', function(done) {
+    registerTestComponent('x-auto-sub1', 'auto-sub1');
+    registerTestComponent('x-auto-sub2', 'auto-sub2');
+    work.innerHTML = '<div></div>';
+    var target = work.firstChild;
+    target.innerHTML = '<div><div><x-auto-sub1></x-auto-sub1><x-auto-sub1></x-auto-sub1>' +
+      '</div></div><div><x-auto-sub2><x-auto-sub1></x-auto-sub1></x-auto-sub2>' +
+      '<x-auto-sub2><x-auto-sub1></x-auto-sub1></x-auto-sub2></div>';
+    customElements.flush();
+    testElements(target, 'x-auto-sub1', 'auto-sub1');
+    testElements(target, 'x-auto-sub2', 'auto-sub2');
+    done();
+  });
+
+  test('CustomElements.upgrade upgrades custom element syntax', function() {
+    registerTestComponent('x-foo31', 'foo');
+    work.innerHTML = '<x-foo31>Foo</x-foo31>';
+    var xfoo = work.firstChild;
+    customElements.flush();
+    assert.equal(xfoo.value, 'foo');
+  });
+
+  test('mutation observer upgrades custom element syntax', function(done) {
+    registerTestComponent('x-foo32', 'foo');
+    work.innerHTML = '<x-foo32>Foo</x-foo32>';
+    customElements.flush();
+    var xfoo = work.firstChild;
+    assert.equal(xfoo.value, 'foo');
+    done();
+  });
+
+  test('document.register upgrades custom element syntax', function() {
+    work.innerHTML = '<x-foo33>Foo</x-foo33>';
+    registerTestComponent('x-foo33', 'foo');
+    var xfoo = work.firstChild;
+    assert.equal(xfoo.value, 'foo');
+  });
+
+  test('CustomElements.upgrade upgrades custom element syntax', function() {
+    registerTestComponent('x-zot', 'zot');
+    registerTestComponent('x-zim', 'zim');
+    work.innerHTML = '<x-zot><x-zim></x-zim></x-zot>';
+    var xzot = work.firstChild, xzim = xzot.firstChild;
+    customElements.flush();
+    assert.equal(xzot.value, 'zot');
+    assert.equal(xzim.value, 'zim');
+  });
+});
diff --git a/tests/CustomElements/v1/runner.html b/tests/CustomElements/v1/runner.html
index c6d3278..08b4007 100644
--- a/tests/CustomElements/v1/runner.html
+++ b/tests/CustomElements/v1/runner.html
@@ -25,7 +25,7 @@
     // 'html/upgrade-dcl.html',
     // 'html/imports.html',
     // 'html/shadowdom.html',
-    // 'js/upgrade.js',
+    'js/upgrade.js',
     // 'js/observe.js',
     // 'js/documentRegister.js',
     // 'html/throttled-attached.html'