diff --git a/includes/form.inc b/includes/form.inc
index 3d5f6f2..b407a5b 100644
--- a/includes/form.inc
+++ b/includes/form.inc
@@ -839,7 +839,9 @@ function drupal_process_form($form_id, &$form, &$form_state) {
     // cache when a form is processed, so scenarios that result in
     // the form being built behind the scenes and again for the
     // browser don't increment all the element IDs needlessly.
-    drupal_static_reset('drupal_html_id');
+    if (!form_get_errors()) {
+      drupal_static_reset('drupal_html_id');
+    }
 
     if ($form_state['submitted'] && !form_get_errors() && !$form_state['rebuild']) {
       // Execute form submit handlers.
diff --git a/modules/simpletest/tests/form.test b/modules/simpletest/tests/form.test
index 13fdca2..6cfb142 100644
--- a/modules/simpletest/tests/form.test
+++ b/modules/simpletest/tests/form.test
@@ -5,6 +5,35 @@
  * 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() {