diff --git a/core/includes/form.inc b/core/includes/form.inc
diff --git a/core/modules/simpletest/tests/form.test b/core/modules/simpletest/tests/form.test
index 784da88..a0cd54d 100644
--- a/core/modules/simpletest/tests/form.test
+++ b/core/modules/simpletest/tests/form.test
@@ -5,6 +5,40 @@
  * Unit tests for the Drupal Form API.
  */
 
+/**
+ * Test duplicates elemens IDs when form validation fails.
+ */
+class FormsDuplicateElementIdsTestCase extends DrupalWebTestCase {
+
+  public static function getInfo() {
+    return array(
+      'name' => 'Duplicates in DOM when form validation fails',
+      'description' => 'Create two form on page and submit one of them.',
+      'group' => 'Form API',
+    );
+  }
+
+  function setUp() {
+    parent::setUp('contact');
+  }
+
+  function testFormValidationFails() {
+
+    // Give anonymous user permission to use contact form
+    user_role_grant_permissions(DRUPAL_ANONYMOUS_RID, array('access site-wide contact form'));
+
+    // Go to page contains contact form
+    $this->drupalGet('contact');
+
+    // Submit contact form
+    $this->drupalPost(NULL, array(), t('Send message'));
+
+    // Check duplicate IDs in DOM
+    $this->assertNoDuplicateIds('There are no duplicate IDs');
+  }
+
+}
+
 class FormsTestCase extends DrupalWebTestCase {
 
   public static function getInfo() {