diff --git a/core/lib/Drupal/Core/Render/Element/Radio.php b/core/lib/Drupal/Core/Render/Element/Radio.php
index ae20284..826431f 100644
--- a/core/lib/Drupal/Core/Render/Element/Radio.php
+++ b/core/lib/Drupal/Core/Render/Element/Radio.php
@@ -37,6 +37,24 @@ public function getInfo() {
     );
   }
 
+ /**
+  * Ensures $element['#default_value'] and $element['#value'] are consistently
+  * typed.
+  *
+  * @param mixed $value
+  *   A value which would be casted.
+  *
+  * @return mixed
+  *   The casted value of the parameter.
+  */
+  protected static function castValue($value)
+  {
+    if (is_bool($value) ||  (int) (bool) $value === (int) $value) {
+      return (string) (int) $value;
+    }
+    return $value;
+  }
+
   /**
    * Prepares a #type 'radio' render element for input.html.twig.
    *
@@ -54,8 +72,16 @@ public static function preRenderRadio($element) {
     $element['#attributes']['type'] = 'radio';
     Element::setAttributes($element, array('id', 'name', '#return_value' => 'value'));
 
-    if (isset($element['#return_value']) && $element['#value'] !== FALSE && $element['#value'] == $element['#return_value']) {
-      $element['#attributes']['checked'] = 'checked';
+    if (isset($element['#return_value']) && $element['#value'] !== FALSE) {
+      // To avoid auto-casting during '==' we convert int 0 to '0' for both
+      // operands. It will prevent wrong true-checking for both cases: 0 ==
+      // 'string' and 'string' == 0.
+      $element['#value'] = static::castValue($element['#value']);
+      $element['#return_value'] = static::castValue($element['#return_value']);
+
+      if ($element['#value'] == $element['#return_value']) {
+        $element['#attributes']['checked'] = 'checked';
+      }
     }
     static::setAttributes($element, array('form-radio'));
 
diff --git a/core/modules/system/src/Tests/Form/ElementTest.php b/core/modules/system/src/Tests/Form/ElementTest.php
index 0ae2edc..50865dd 100644
--- a/core/modules/system/src/Tests/Form/ElementTest.php
+++ b/core/modules/system/src/Tests/Form/ElementTest.php
@@ -89,6 +89,26 @@ function testOptions() {
   }
 
   /**
+   * Tests correct checked attribute for radios element.
+   */
+  function testRadiosChecked() {
+    // Verify that there is only one radio option checked.
+    $this->drupalGet('form-test/radios-checked');
+    $elements = $this->xpath('//input[@name="radios" and @checked]');
+    $this->assertEqual(count($elements), 1);
+    $this->assertIdentical((string) $elements[0]['value'], '0');
+    $elements = $this->xpath('//input[@name="radios-string" and @checked]');
+    $this->assertEqual(count($elements), 1);
+    $this->assertIdentical((string) $elements[0]['value'], 'bar');
+    $elements = $this->xpath('//input[@name="radios-boolean-true" and @checked]');
+    $this->assertEqual(count($elements), 1);
+    $this->assertIdentical((string) $elements[0]['value'], '1');
+    // A default value of FALSE indicates that nothing is set.
+    $elements = $this->xpath('//input[@name="radios-boolean-false" and @checked]');
+    $this->assertEqual(count($elements), 0);
+  }
+
+  /**
    * Tests wrapper ids for checkboxes and radios.
    */
   function testWrapperIds() {
diff --git a/core/modules/system/tests/modules/form_test/form_test.routing.yml b/core/modules/system/tests/modules/form_test/form_test.routing.yml
index 2250a0b..0ee125c 100644
--- a/core/modules/system/tests/modules/form_test/form_test.routing.yml
+++ b/core/modules/system/tests/modules/form_test/form_test.routing.yml
@@ -294,6 +294,14 @@ form_test.checkboxes_radios:
   requirements:
     _access: 'TRUE'
 
+form_test.radios_checked:
+  path: '/form-test/radios-checked'
+  defaults:
+    _form: '\Drupal\form_test\Form\FormTestRadiosCheckedForm'
+    _title: 'Radios checked defalt value'
+  requirements:
+    _access: 'TRUE'
+
 form_test.email:
   path: '/form-test/email'
   defaults:
diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestRadiosCheckedForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestRadiosCheckedForm.php
new file mode 100644
index 0000000..c46bd8c
--- /dev/null
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestRadiosCheckedForm.php
@@ -0,0 +1,82 @@
+<?php
+
+namespace Drupal\form_test\Form;
+
+use Drupal\Core\Form\FormBase;
+use Drupal\Core\Form\FormStateInterface;
+use Symfony\Component\HttpFoundation\JsonResponse;
+
+/**
+ * Form constructor to test #default_value settings of radios.
+ */
+class FormTestRadiosCheckedForm extends FormBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFormId() {
+    return 'form_test_radios_checked';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildForm(array $form, FormStateInterface $form_state) {
+    $form['radios'] = array(
+      '#type' => 'radios',
+      '#title' => 'Radios',
+      '#options' => array(
+        0 => 'Zero',
+        'foo' => 'Foo',
+        1 => 'One',
+        'bar' => '<em>Bar - radios</em>',
+        '>' => "<em>Special Char</em><script>alert('radios');</script>",
+      ),
+      '#default_value' => 0,
+    );
+    $form['radios-string'] = array(
+      '#type' => 'radios',
+      '#title' => 'Radios',
+      '#options' => array(
+        0 => 'Zero',
+        'foo' => 'Foo',
+        1 => 'One',
+        'bar' => '<em>Bar - radios</em>',
+        '>' => "<em>Special Char</em><script>alert('radios');</script>",
+      ),
+      '#default_value' => 'bar',
+    );
+    $form['radios-boolean-true'] = array(
+      '#type' => 'radios',
+      '#title' => 'Radios',
+      '#options' => array(
+        'All' => '- Any -',
+        1 => 'True',
+        0 => 'False',
+      ),
+      '#default_value' => TRUE,
+    );
+    $form['radios-boolean-false'] = array(
+      '#type' => 'radios',
+      '#title' => 'Radios',
+      '#options' => array(
+        'All' => '- Any -',
+        1 => 'True',
+        0 => 'False',
+      ),
+      '#default_value' => FALSE,
+    );
+
+    $form['submit'] = array('#type' => 'submit', '#value' => 'Submit');
+
+    return $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitForm(array &$form, FormStateInterface $form_state) {
+    $form_state->setResponse(new JsonResponse($form_state->getValues()));
+  }
+
+}
diff --git a/core/modules/views_ui/src/Tests/DisplayTest.php b/core/modules/views_ui/src/Tests/DisplayTest.php
index 7f5f125..2976120 100644
--- a/core/modules/views_ui/src/Tests/DisplayTest.php
+++ b/core/modules/views_ui/src/Tests/DisplayTest.php
@@ -163,7 +163,9 @@ public function testLinkDisplay() {
     $this->assertEqual($result[0], t('None'), 'Make sure that the link option summary shows "None" by default.');
 
     $this->drupalGet($link_display_path);
-    $this->assertFieldChecked('edit-link-display-0');
+    // We are looking for the None option which has a '' key, that's why there
+    // is no key appended in the ID.
+    $this->assertFieldChecked('edit-link-display-');
 
     // Test the default radio option on the link display form.
     $this->drupalPostForm($link_display_path, array('link_display' => 'page_1'), t('Apply'));
diff --git a/core/tests/Drupal/Tests/Core/Render/Element/RadioTest.php b/core/tests/Drupal/Tests/Core/Render/Element/RadioTest.php
new file mode 100644
index 0000000..7381cfa
--- /dev/null
+++ b/core/tests/Drupal/Tests/Core/Render/Element/RadioTest.php
@@ -0,0 +1,29 @@
+<?php
+
+namespace Drupal\Tests\Core\Render\Element;
+
+use Drupal\Core\Render\Element\Radio;
+use Drupal\Tests\UnitTestCase;
+
+/**
+ * @coversDefaultClass \Drupal\Core\Render\Element\Radio
+ * @group Render
+ */
+class RadioTest extends UnitTestCase {
+
+  /**
+   * @covers ::preRenderRadio
+   */
+  public function testPreRenderRadio() {
+    $element = [
+      '#return_value' => 0,
+      '#value' => 'All',
+      '#attributes' => [],
+    ];
+
+    $element = Radio::preRenderRadio($element);
+
+    $this->assertArrayNotHasKey('checked', $element['#attributes']);
+  }
+
+}