diff --git a/core/modules/simpletest/tests/form.test b/core/modules/simpletest/tests/form.test
index 49933c3..222549a 100644
--- a/core/modules/simpletest/tests/form.test
+++ b/core/modules/simpletest/tests/form.test
@@ -129,6 +129,7 @@ class FormsTestCase extends DrupalWebTestCase {
    * and each is checked for the proper #required error messages.
    *
    * @see form_test_validate_required_form()
+   * @see form_test_element_validate()
    */
   function testRequiredCheckboxesRadio() {
     $form = $form_state = array();
@@ -142,10 +143,13 @@ class FormsTestCase extends DrupalWebTestCase {
       $this->assertText(t('!name field is required.', array('!name' => $form[$key]['#title'])));
     }
 
-    // The unhelpful catch-all generic error should not appear.
-    $this->assertNoText(t('An illegal choice has been detected. Please contact the site administrator.'));
+    // No invalid options were submitted, only empty ones. Therefore, the error
+    // message about disallowed values should not appear, nor should our custom
+    // validator report that the value is not found.
+    $this->assertNoText(t('illegal choice'));
+    $this->assertNoText(t('Value is not allowed'));
 
-    // Verify that no error appears with valid values.
+    // Verify that no errors appear with valid values.
     $edit = array(
       'textfield' => $this->randomString(),
       'checkboxes[foo]' => TRUE,
@@ -157,7 +161,8 @@ class FormsTestCase extends DrupalWebTestCase {
     foreach (array('textfield', 'checkboxes', 'select', 'radios') as $key) {
       $this->assertNoText(t('!name field is required.', array('!name' => $form[$key]['#title'])));
     }
-    $this->assertNoText(t('An illegal choice has been detected. Please contact the site administrator.'));
+    $this->assertNoText(t('illegal choice'));
+    $this->assertNoText(t('Value is not allowed'));
   }
 
   /**
diff --git a/core/modules/simpletest/tests/form_test.module b/core/modules/simpletest/tests/form_test.module
index 73bda37..6f57d92 100644
--- a/core/modules/simpletest/tests/form_test.module
+++ b/core/modules/simpletest/tests/form_test.module
@@ -359,29 +359,34 @@ function form_test_validate_required_form($form, &$form_state) {
     '#type' => 'textfield',
     '#title' => 'Textfield',
     '#required' => TRUE,
+    '#element_validate' => array('form_test_element_validate'),
   );
   $form['checkboxes'] = array(
     '#type' => 'checkboxes',
     '#title' => 'Checkboxes',
     '#options' => drupal_map_assoc(array('foo', 'bar')),
     '#required' => TRUE,
+    '#element_validate' => array('form_test_element_validate'),
   );
   $form['select'] = array(
     '#type' => 'select',
     '#title' => 'Select',
     '#options' => drupal_map_assoc(array('foo', 'bar')),
     '#required' => TRUE,
+    '#element_validate' => array('form_test_element_validate'),
   );
   $form['radios'] = array(
     '#type' => 'radios',
     '#title' => 'Radios',
     '#options' => drupal_map_assoc(array('foo', 'bar')),
     '#required' => TRUE,
+    '#element_validate' => array('form_test_element_validate'),
   );
   $form['radios_optional'] = array(
     '#type' => 'radios',
     '#title' => 'Radios (optional)',
     '#options' => drupal_map_assoc(array('foo', 'bar')),
+    '#element_validate' => array('form_test_element_validate'),
   );
   $form['actions'] = array('#type' => 'actions');
   $form['actions']['submit'] = array('#type' => 'submit', '#value' => 'Submit');
@@ -389,6 +394,37 @@ function form_test_validate_required_form($form, &$form_state) {
 }
 
 /**
+ * Form element validation handler for form_test_validate_required_form().
+ *
+ * Checks the form element for values that are not in the allowed values,
+ * using logic from _form_validate().
+ */
+function form_test_element_validate($element, &$form_state, $form) {
+  if (isset($element['#options']) && isset($element['#value'])) {
+    if ($element['#type'] == 'select') {
+      $options = form_options_flatten($element['#options']);
+    }
+    else {
+      $options = $element['#options'];
+    }
+    if (is_array($element['#value'])) {
+      $value = in_array($element['#type'], array('checkboxes', 'tableselect')) ? array_keys($element['#value']) : $element['#value'];
+      foreach ($value as $v) {
+        if (!isset($options[$v])) {
+          drupal_set_message("Value is not allowed for {$element['#name']}.");
+        }
+      }
+    }
+    elseif ($element['#type'] == 'select' && !$element['#multiple'] && $element['#required'] && !isset($element['#default_value']) && $element['#value'] === $element['#empty_value']) {
+      drupal_set_message("Value is not allowed for {$element['#name']}.");
+    }
+    elseif (!isset($options[$element['#value']])) {
+      drupal_set_message("Value is not allowed for {$element['#name']}.");
+    }
+  }
+}
+
+/**
  * Builds a simple form with a button triggering partial validation.
  */
 function form_test_limit_validation_errors_form($form, &$form_state) {