diff --git a/core/modules/config/lib/Drupal/config/Tests/ConfigOverrideTest.php b/core/modules/config/lib/Drupal/config/Tests/ConfigOverrideTest.php
index de7784f..8e83a84 100644
--- a/core/modules/config/lib/Drupal/config/Tests/ConfigOverrideTest.php
+++ b/core/modules/config/lib/Drupal/config/Tests/ConfigOverrideTest.php
@@ -43,21 +43,25 @@ function testConfOverride() {
     $expected_original_data = array(
       'foo' => 'bar',
       'baz' => NULL,
+      '404' => 'herp',
     );
 
     // Verify that the original configuration data exists.
     $config = config('config_test.system');
     $this->assertIdentical($config->get('foo'), $expected_original_data['foo']);
     $this->assertIdentical($config->get('baz'), $expected_original_data['baz']);
+    $this->assertIdentical($config->get('404'), $expected_original_data['404']);
 
     // Apply the overridden data.
     $conf['config_test.system']['foo'] = 'overridden';
     $conf['config_test.system']['baz'] = 'injected';
+    $conf['config_test.system']['404'] = 'derp';
 
     // Verify that the in-memory configuration object still contains the
     // original data.
     $this->assertIdentical($config->get('foo'), $expected_original_data['foo']);
     $this->assertIdentical($config->get('baz'), $expected_original_data['baz']);
+    $this->assertIdentical($config->get('404'), $expected_original_data['404']);
 
     // Reload the configuration object.
     $config = config('config_test.system');
@@ -65,14 +69,20 @@ function testConfOverride() {
     // Verify that it contains the overridden data from $conf.
     $this->assertIdentical($config->get('foo'), $conf['config_test.system']['foo']);
     $this->assertIdentical($config->get('baz'), $conf['config_test.system']['baz']);
+    $this->assertIdentical($config->get('404'), $conf['config_test.system']['404']);
 
     // Set the value for 'baz' (on the original data).
     $expected_original_data['baz'] = 'original baz';
     $config->set('baz', $expected_original_data['baz']);
 
+    // Set the value for '404' (on the original data).
+    $expected_original_data['404'] = 'original 404';
+    $config->set('404', $expected_original_data['404']);
+
     // Verify that it still contains the overridden data from $conf.
     $this->assertIdentical($config->get('foo'), $conf['config_test.system']['foo']);
     $this->assertIdentical($config->get('baz'), $conf['config_test.system']['baz']);
+    $this->assertIdentical($config->get('404'), $conf['config_test.system']['404']);
 
     // Save the configuration object (having overrides applied).
     $config->save();
@@ -81,6 +91,7 @@ function testConfOverride() {
     $config = config('config_test.system');
     $this->assertIdentical($config->get('foo'), $conf['config_test.system']['foo']);
     $this->assertIdentical($config->get('baz'), $conf['config_test.system']['baz']);
+    $this->assertIdentical($config->get('404'), $conf['config_test.system']['404']);
 
     // Remove the $conf overrides.
     unset($conf['config_test.system']);
@@ -89,6 +100,7 @@ function testConfOverride() {
     $config = config('config_test.system');
     $this->assertIdentical($config->get('foo'), $expected_original_data['foo']);
     $this->assertIdentical($config->get('baz'), $expected_original_data['baz']);
+    $this->assertIdentical($config->get('404'), $expected_original_data['404']);
   }
 
 }
diff --git a/core/modules/config/tests/config_test/config/config_test.system.yml b/core/modules/config/tests/config_test/config/config_test.system.yml
index 20e9ff3..c34eddf 100644
--- a/core/modules/config/tests/config_test/config/config_test.system.yml
+++ b/core/modules/config/tests/config_test/config/config_test.system.yml
@@ -1 +1,2 @@
 foo: bar
+404: herp