diff --git a/core/modules/simpletest/tests/form.test b/core/modules/simpletest/tests/form.test
index c67e57a..0edd209 100644
--- a/core/modules/simpletest/tests/form.test
+++ b/core/modules/simpletest/tests/form.test
@@ -802,6 +802,16 @@ class FormValidationTestCase extends DrupalWebTestCase {
     $this->drupalPost('form-test/pattern', $edit, 'Submit');
     $this->assertNoRaw($textfield_error);
     $this->assertNoRaw($tel_error);
+
+    // The pattern attribute overrides #pattern and is not validated on the
+    // server side.
+    $edit = array(
+      'textfield' => '',
+      'tel' => '',
+      'url' => 'http://www.example.com/',
+    );
+    $this->drupalPost('form-test/pattern', $edit, 'Submit');
+    $this->assertNoRaw(t('%name field is not in the right format.', array('%name' => 'Client side validation')));
   }
 }
 
diff --git a/core/modules/simpletest/tests/form_test.module b/core/modules/simpletest/tests/form_test.module
index 532325f..0d36149 100644
--- a/core/modules/simpletest/tests/form_test.module
+++ b/core/modules/simpletest/tests/form_test.module
@@ -533,6 +533,15 @@ function form_test_pattern_form($form, &$form_state) {
     '#title' => 'Everything except numbers',
     '#pattern' => '[^\d]*',
   );
+  $form['url'] = array(
+    '#type' => 'url',
+    '#title' => 'Client side validation',
+    '#decription' => 'Just client side validation, using the #pattern attribute.',
+    '#attributes' => array(
+      'pattern' => '.*foo.*',
+    ),
+    '#pattern' => 'ignored',
+  );
   $form['submit'] = array(
     '#type' => 'submit',
     '#value' => 'Submit',