diff --git a/src/lib/dom-api-shadow.html b/src/lib/dom-api-shadow.html
index 3cdb7ea8fd..daf15df8d9 100644
--- a/src/lib/dom-api-shadow.html
+++ b/src/lib/dom-api-shadow.html
@@ -60,11 +60,13 @@
 
     activeElement: {
       get: function() {
-        return Polymer.DomApi.wrap(this.node).activeElement;
+        var node = Polymer.DomApi.wrap(this.node);
+        var activeElement = node.activeElement;
+        return node.contains(activeElement) ? activeElement : null;
       },
       configurable: true
     },
-    
+
     childNodes: {
       get: function() {
         return TreeApi.arrayCopyChildNodes(this.node);
diff --git a/src/lib/dom-api-shady.html b/src/lib/dom-api-shady.html
index 9d00661e95..ccb9335429 100644
--- a/src/lib/dom-api-shady.html
+++ b/src/lib/dom-api-shady.html
@@ -430,35 +430,35 @@
         }
         var isShadyRoot = !!this.node._isShadyRoot;
         if (this.node !== document) {
-          // If this node isn't a document or shady root, then it doesn't
-          // have an active element.
+          // If this node isn't a document or shady root, then it doesn't have
+          // an active element.
           if (!isShadyRoot) {
             return null;
           }
           // If this shady root's host is the active element or the active
-          // element is not a descendant of the host, then it doesn't have
-          // an active element.
+          // element is not a descendant of the host (in the composed tree),
+          // then it doesn't have an active element.
           if (this.node.host === active ||
               !this.node.host.contains(active)) {
             return null;
           }
-          // If the active element is a light descendant of the shady root's
-          // host, return the active element.
-          if (this.node.host !== active &&
-              this._contains(this.node.host, active)) {
-            return active;
-          }
         }
-        // This node is either the document or a shady root of which the
-        // active element is a descendant of its host; iterate upwards to
-        // find the active element's most shallow host.
+        // This node is either the document or a shady root of which the active
+        // element is a (composed) descendant of its host; iterate upwards to
+        // find the active element's most shallow host within it.
         var activeRoot = Polymer.dom(active).getOwnerRoot();
-        while (activeRoot && activeRoot !== this.node &&
-            !(isShadyRoot && this._contains(this.node.host, active))) {
+        while (activeRoot && activeRoot !== this.node) {
           active = activeRoot.host;
           activeRoot = Polymer.dom(active).getOwnerRoot();
         }
-        return active;
+        if (this.node === document) {
+          // This node is the document, so activeRoot should be null.
+          return activeRoot ? null : active;
+        } else {
+          // This node is a non-document shady root, and it should be
+          // activeRoot.
+          return activeRoot === this.node ? active : null;
+        }
       },
       configurable: true
     },
diff --git a/test/unit/polymer-dom.js b/test/unit/polymer-dom.js
index f6e06747ea..ab9f735d7f 100644
--- a/test/unit/polymer-dom.js
+++ b/test/unit/polymer-dom.js
@@ -868,7 +868,7 @@ suite('Polymer.dom accessors', function() {
       r_l.focus();
 
       assert.equal(Polymer.dom(document).activeElement, r_l, 'document.activeElement === r_l');
-      assert.equal(Polymer.dom(r.root).activeElement, r_l, 'r.root.activeElement === r_l');
+      assert.equal(Polymer.dom(r.root).activeElement, null, 'r.root.activeElement === null');
       assert.equal(Polymer.dom(r_0.root).activeElement, null, 'r_0.root.activeElement === null');
       assert.equal(Polymer.dom(r_0_0.root).activeElement, null, 'r_0_0.root.activeElement === null');
       assert.equal(Polymer.dom(r_0_1.root).activeElement, null, 'r_0_1.root.activeElement === null');
@@ -895,7 +895,7 @@ suite('Polymer.dom accessors', function() {
 
       assert.equal(Polymer.dom(document).activeElement, r, 'document.activeElement === r');
       assert.equal(Polymer.dom(r.root).activeElement, r_0_l, 'r.root.activeElement === r_0_l');
-      assert.equal(Polymer.dom(r_0.root).activeElement, r_0_l, 'r_0.root.activeElement === r_0_l');
+      assert.equal(Polymer.dom(r_0.root).activeElement, null, 'r_0.root.activeElement === null');
       assert.equal(Polymer.dom(r_1.root).activeElement, null, 'r_1.root.activeElement === null');
 
       assert.equal(Polymer.dom(r_0_0.root).activeElement, null, 'r_0_0.root.activeElement === null');
@@ -923,7 +923,7 @@ suite('Polymer.dom accessors', function() {
       assert.equal(Polymer.dom(document).activeElement, r, 'document.activeElement === r');
       assert.equal(Polymer.dom(r.root).activeElement, r_0, 'r.root.activeElement === r_0');
       assert.equal(Polymer.dom(r_0.root).activeElement, r_0_0_l, 'r_0.root.activeElement === r_0_0_l');
-      assert.equal(Polymer.dom(r_0_0.root).activeElement, r_0_0_l, 'r_0_0.root.activeElement === r_0_0_l');
+      assert.equal(Polymer.dom(r_0_0.root).activeElement, null, 'r_0_0.root.activeElement === null');
       assert.equal(Polymer.dom(r_0_1.root).activeElement, null, 'r_0_1.root.activeElement === null');
       assert.equal(Polymer.dom(r_1.root).activeElement, null, 'r_1.root.activeElement === null');
       assert.equal(Polymer.dom(r_1_0.root).activeElement, null, 'r_1_0.root.activeElement === null');
@@ -936,7 +936,7 @@ suite('Polymer.dom accessors', function() {
       assert.equal(Polymer.dom(document).activeElement, r, 'document.activeElement === r');
       assert.equal(Polymer.dom(r.root).activeElement, r_0, 'r.root.activeElement === r_0');
       assert.equal(Polymer.dom(r_0.root).activeElement, r_0_0_l, 'r_0.root.activeElement === r_0_0_l');
-      assert.equal(Polymer.dom(r_0_0.root).activeElement, r_0_0_l, 'r_0_0.root.activeElement === r_0_0_l');
+      assert.equal(Polymer.dom(r_0_0.root).activeElement, null, 'r_0_0.root.activeElement === null');
       assert.equal(Polymer.dom(r_0_0_l.root).activeElement, r_0_0_l_0, 'r_0_0_l.root.activeElement === r_0_0_l_0');
       assert.equal(Polymer.dom(r_0_1.root).activeElement, null, 'r_0_1.root.activeElement === null');
       assert.equal(Polymer.dom(r_1.root).activeElement, null, 'r_1.root.activeElement === null');
@@ -964,7 +964,7 @@ suite('Polymer.dom accessors', function() {
       assert.equal(Polymer.dom(r.root).activeElement, r_0, 'r.root.activeElement === r_0');
       assert.equal(Polymer.dom(r_0.root).activeElement, r_0_1_l, 'r_0.root.activeElement === r_0_1_l');
       assert.equal(Polymer.dom(r_0_0.root).activeElement, null, 'r_0_0.root.activeElement === null');
-      assert.equal(Polymer.dom(r_0_1.root).activeElement, r_0_1_l, 'r_0_1.root.activeElement === r_0_1_l');
+      assert.equal(Polymer.dom(r_0_1.root).activeElement, null, 'r_0_1.root.activeElement === null');
       assert.equal(Polymer.dom(r_1.root).activeElement, null, 'r_1.root.activeElement === null');
       assert.equal(Polymer.dom(r_1_0.root).activeElement, null, 'r_1_0.root.activeElement === null');
       assert.equal(Polymer.dom(r_1_1.root).activeElement, null, 'r_1_1.root.activeElement === null');
@@ -991,7 +991,7 @@ suite('Polymer.dom accessors', function() {
       assert.equal(Polymer.dom(r_0.root).activeElement, null, 'r_0.root.activeElement === null');
       assert.equal(Polymer.dom(r_0_0.root).activeElement, null, 'r_0_0.root.activeElement === null');
       assert.equal(Polymer.dom(r_0_1.root).activeElement, null, 'r_0_1.root.activeElement === null');
-      assert.equal(Polymer.dom(r_1.root).activeElement, r_1_l, 'r_1.root.activeElement === r_1_l');
+      assert.equal(Polymer.dom(r_1.root).activeElement, null, 'r_1.root.activeElement === null');
       assert.equal(Polymer.dom(r_1_0.root).activeElement, null, 'r_1_0.root.activeElement === null');
       assert.equal(Polymer.dom(r_1_1.root).activeElement, null, 'r_1_1.root.activeElement === null');
     });
@@ -1004,7 +1004,7 @@ suite('Polymer.dom accessors', function() {
       assert.equal(Polymer.dom(r_0.root).activeElement, null, 'r_0.root.activeElement === null');
       assert.equal(Polymer.dom(r_0_0.root).activeElement, null, 'r_0_0.root.activeElement === null');
       assert.equal(Polymer.dom(r_0_1.root).activeElement, null, 'r_0_1.root.activeElement === null');
-      assert.equal(Polymer.dom(r_1.root).activeElement, r_1_l, 'r_1.root.activeElement === r_1_l');
+      assert.equal(Polymer.dom(r_1.root).activeElement, null, 'r_1.root.activeElement === null');
       assert.equal(Polymer.dom(r_1_l.root).activeElement, r_1_l_0, 'r_1.root.activeElement === r_1_l_0');
       assert.equal(Polymer.dom(r_1_0.root).activeElement, null, 'r_1_0.root.activeElement === null');
       assert.equal(Polymer.dom(r_1_1.root).activeElement, null, 'r_1_1.root.activeElement === null');
@@ -1032,7 +1032,7 @@ suite('Polymer.dom accessors', function() {
       assert.equal(Polymer.dom(r_0_0.root).activeElement, null, 'r_0_0.root.activeElement === null');
       assert.equal(Polymer.dom(r_0_1.root).activeElement, null, 'r_0_1.root.activeElement === null');
       assert.equal(Polymer.dom(r_1.root).activeElement, r_1_0_l, 'r_1.root.activeElement === r_1_0_l');
-      assert.equal(Polymer.dom(r_1_0.root).activeElement, r_1_0_l, 'r_1_0.root.activeElement === r_1_0_l');
+      assert.equal(Polymer.dom(r_1_0.root).activeElement, null, 'r_1_0.root.activeElement === null');
       assert.equal(Polymer.dom(r_1_1.root).activeElement, null, 'r_1_1.root.activeElement === null');
     });
 
@@ -1059,7 +1059,7 @@ suite('Polymer.dom accessors', function() {
       assert.equal(Polymer.dom(r_0_1.root).activeElement, null, 'r_0_1.root.activeElement === null');
       assert.equal(Polymer.dom(r_1.root).activeElement, r_1_1_l, 'r_1.root.activeElement === r_1_1_l');
       assert.equal(Polymer.dom(r_1_0.root).activeElement, null, 'r_1_0.root.activeElement === null');
-      assert.equal(Polymer.dom(r_1_1.root).activeElement, r_1_1_l, 'r_1_1.root.activeElement === r_1_1_l');
+      assert.equal(Polymer.dom(r_1_1.root).activeElement, null, 'r_1_1.root.activeElement === null');
     });
 
     test('setting activeElement on document has no effect', function() {