diff --git a/dom/datastore/DataStore.jsm b/dom/datastore/DataStore.jsm
index 115642ee56a..a4418d3f857 100644
--- a/dom/datastore/DataStore.jsm
+++ b/dom/datastore/DataStore.jsm
@@ -36,7 +36,7 @@ XPCOMUtils.defineLazyServiceGetter(this, "cpmm",
 
 /* Helper functions */
 function createDOMError(aWindow, aEvent) {
-  return new aWindow.DOMError(aEvent.target.error.name);
+  return new aWindow.DOMError(aEvent);
 }
 
 function throwInvalidArg(aWindow) {
diff --git a/dom/datastore/tests/file_duplicate.html b/dom/datastore/tests/file_duplicate.html
new file mode 100644
index 00000000000..3a45c2535b9
--- /dev/null
+++ b/dom/datastore/tests/file_duplicate.html
@@ -0,0 +1,75 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <meta charset="utf-8">
+  <title>Test for DataStore - duplicate keys</title>
+</head>
+<body>
+<div id="container"></div>
+  <script type="application/javascript;version=1.7">
+
+  var gStore;
+  var gEvent;
+  var gChangeId;
+
+  function ok(a, msg) {
+    alert((a ? 'OK' : 'KO')+ ' ' + msg)
+  }
+
+  function is(a, b, msg) {
+    ok(a === b, msg);
+  }
+
+  function cbError() {
+    alert('KO error');
+  }
+
+  function finish() {
+    alert('DONE');
+  }
+
+  function testGetDataStores() {
+    navigator.getDataStores('foo').then(function(stores) {
+      gStore = stores[0];
+      runTest();
+    }, cbError);
+  }
+
+  function testAdd(success) {
+    gStore.add({ a: 42 }, 'test').then(function() {
+      is(success, true, "Record added");
+      runTest();
+    }, function(e) {
+      is(success, false, "Record failed");
+      ok(e instanceof DOMError, "DOMError received");
+      is(e.name, 'ConstraintError', 'e.name: ConstraintError');
+      is(e.message, '', 'e.message');
+      runTest();
+    });
+  }
+
+  var tests = [
+    // Test for GetDataStore
+    testGetDataStores,
+
+    // add
+    function() { testAdd(true); },
+
+    // add duplicate
+    function() { testAdd(false); }
+  ];
+
+  function runTest() {
+    if (!tests.length) {
+      finish();
+      return;
+    }
+
+    var test = tests.shift();
+    test();
+  }
+
+  runTest();
+  </script>
+</body>
+</html>
diff --git a/dom/datastore/tests/mochitest.ini b/dom/datastore/tests/mochitest.ini
index abc78f3862f..cf65f24ce77 100644
--- a/dom/datastore/tests/mochitest.ini
+++ b/dom/datastore/tests/mochitest.ini
@@ -13,6 +13,7 @@ support-files =
   file_bug924104.html
   file_certifiedApp.html
   file_keys.html
+  file_duplicate.html
 
 [test_app_install.html]
 [test_readonly.html]
@@ -24,3 +25,4 @@ support-files =
 [test_bug924104.html]
 [test_certifiedApp.html]
 [test_keys.html]
+[test_duplicate.html]
diff --git a/dom/datastore/tests/test_duplicate.html b/dom/datastore/tests/test_duplicate.html
new file mode 100644
index 00000000000..1f14f9a74b9
--- /dev/null
+++ b/dom/datastore/tests/test_duplicate.html
@@ -0,0 +1,128 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <meta charset="utf-8">
+  <title>Test for DataStore - duplicate keys</title>
+  <script type="application/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<div id="container"></div>
+  <script type="application/javascript;version=1.7">
+
+  var gHostedManifestURL = 'http://test/tests/dom/datastore/tests/file_app.sjs?testToken=file_duplicate.html';
+  var gApp;
+
+  function cbError() {
+    ok(false, "Error callback invoked");
+    finish();
+  }
+
+  function installApp() {
+    var request = navigator.mozApps.install(gHostedManifestURL);
+    request.onerror = cbError;
+    request.onsuccess = function() {
+      gApp = request.result;
+      runTest();
+    }
+  }
+
+  function uninstallApp() {
+    // Uninstall the app.
+    var request = navigator.mozApps.mgmt.uninstall(gApp);
+    request.onerror = cbError;
+    request.onsuccess = function() {
+      // All done.
+      info("All done");
+      runTest();
+    }
+  }
+
+  function testApp() {
+    var ifr = document.createElement('iframe');
+    ifr.setAttribute('mozbrowser', 'true');
+    ifr.setAttribute('mozapp', gApp.manifestURL);
+    ifr.setAttribute('src', gApp.manifest.launch_path);
+    var domParent = document.getElementById('container');
+
+    // Set us up to listen for messages from the app.
+    var listener = function(e) {
+      var message = e.detail.message;
+      if (/^OK/.exec(message)) {
+        ok(true, "Message from app: " + message);
+      } else if (/KO/.exec(message)) {
+        ok(false, "Message from app: " + message);
+      } else if (/DONE/.exec(message)) {
+        ok(true, "Messaging from app complete");
+        ifr.removeEventListener('mozbrowsershowmodalprompt', listener);
+        domParent.removeChild(ifr);
+        runTest();
+      }
+    }
+
+    // This event is triggered when the app calls "alert".
+    ifr.addEventListener('mozbrowsershowmodalprompt', listener, false);
+    domParent.appendChild(ifr);
+  }
+
+  var tests = [
+    // Permissions
+    function() {
+      SpecialPowers.pushPermissions(
+        [{ "type": "browser", "allow": 1, "context": document },
+         { "type": "embed-apps", "allow": 1, "context": document },
+         { "type": "webapps-manage", "allow": 1, "context": document }], runTest);
+    },
+
+    // Preferences
+    function() {
+      SpecialPowers.pushPrefEnv({"set": [["dom.promise.enabled", true],
+                                         ["dom.datastore.enabled", true],
+                                         ["dom.testing.ignore_ipc_principal", true],
+                                         ["dom.testing.datastore_enabled_for_hosted_apps", true]]}, runTest);
+    },
+
+    function() {
+      SpecialPowers.setAllAppsLaunchable(true);
+      SpecialPowers.setBoolPref("dom.mozBrowserFramesEnabled", true);
+      runTest();
+    },
+
+    // No confirmation needed when an app is installed
+    function() {
+      SpecialPowers.autoConfirmAppInstall(runTest);
+    },
+
+    // Installing the app
+    installApp,
+
+    // Run tests in app
+    testApp,
+
+    // Uninstall the app
+    uninstallApp
+  ];
+
+  function runTest() {
+    if (!tests.length) {
+      finish();
+      return;
+    }
+
+    var test = tests.shift();
+    test();
+  }
+
+  function finish() {
+    SimpleTest.finish();
+  }
+
+  if (SpecialPowers.isMainProcess()) {
+    SpecialPowers.Cu.import("resource://gre/modules/DataStoreChangeNotifier.jsm");
+  }
+
+  SimpleTest.waitForExplicitFinish();
+  runTest();
+  </script>
+</body>
+</html>
