diff -u b/core/lib/Drupal/Core/Render/Element/Radio.php b/core/lib/Drupal/Core/Render/Element/Radio.php
--- b/core/lib/Drupal/Core/Render/Element/Radio.php
+++ b/core/lib/Drupal/Core/Render/Element/Radio.php
@@ -54,17 +54,17 @@
     $element['#attributes']['type'] = 'radio';
     Element::setAttributes($element, array('id', 'name', '#return_value' => 'value'));
 
-    if (isset($element['#return_value'])) {
+    if (isset($element['#return_value']) &&  $element['#value'] !== FALSE) {
       // To avoid auto-casting during '==' we convert int 0 to '0' for both
       // operands. It will prevent wrong true-checking for both cases: 0 ==
       // 'string' and 'string' == 0.
-      if ($element['#value'] === 0 || $element['#value'] === FALSE) {
+      if ($element['#value'] === 0) {
         $element['#value'] = '0';
       }
       elseif ($element['#value'] === TRUE) {
         $element['#value'] = '1';
       }
-      if ($element['#return_value'] === 0 || $element['#return_value'] === FALSE) {
+      if ($element['#return_value'] === 0) {
         $element['#return_value'] = '0';
       }
       elseif ($element['#return_value'] === TRUE) {
diff -u b/core/modules/system/src/Tests/Form/ElementTest.php b/core/modules/system/src/Tests/Form/ElementTest.php
--- b/core/modules/system/src/Tests/Form/ElementTest.php
+++ b/core/modules/system/src/Tests/Form/ElementTest.php
@@ -103,9 +103,9 @@
     $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), 1);
-    $this->assertIdentical((string) $elements[0]['value'], '0');
+    $this->assertEqual(count($elements), 0);
   }
 
   /**