diff --git a/core/lib/Drupal/Core/Config/Config.php b/core/lib/Drupal/Core/Config/Config.php
index 02afbd1..1e180cd 100644
--- a/core/lib/Drupal/Core/Config/Config.php
+++ b/core/lib/Drupal/Core/Config/Config.php
@@ -207,6 +207,8 @@ public function isNew() {
    *   A key of 'foo.bar' would return the string 'baz'. However, a key of 'foo'
    *   would return array('bar' => 'baz').
    *   If no key is specified, then the entire data array is returned.
+   * @param mixed $default
+   *   (optional) A default value to return if no value is found.
    *
    * The configuration system does not retain data types. Every saved value is
    * casted to a string. In most cases this is not an issue; however, it can
@@ -218,7 +220,7 @@ public function isNew() {
    * @return mixed
    *   The data that was requested.
    */
-  public function get($key = '') {
+  public function get($key = '', $default = NULL) {
     if (!$this->isLoaded) {
       $this->load();
     }
@@ -231,11 +233,11 @@ public function get($key = '') {
     else {
       $parts = explode('.', $key);
       if (count($parts) == 1) {
-        return isset($this->overriddenData[$key]) ? $this->overriddenData[$key] : NULL;
+        return isset($this->overriddenData[$key]) ? $this->overriddenData[$key] : $default;
       }
       else {
         $value = NestedArray::getValue($this->overriddenData, $parts, $key_exists);
-        return $key_exists ? $value : NULL;
+        return $key_exists ? $value : $default;
       }
     }
   }
diff --git a/core/modules/config/lib/Drupal/config/Tests/ConfigCRUDTest.php b/core/modules/config/lib/Drupal/config/Tests/ConfigCRUDTest.php
index 363b889..05d38b6 100644
--- a/core/modules/config/lib/Drupal/config/Tests/ConfigCRUDTest.php
+++ b/core/modules/config/lib/Drupal/config/Tests/ConfigCRUDTest.php
@@ -40,6 +40,13 @@ function testCRUD() {
     $config = \Drupal::config($name);
     $this->assertIdentical($config->isNew(), TRUE);
 
+    // Verify the correct default values are returned for non-existent keys.
+    $this->assertIdentical($config->get('non-existent'), NULL);
+    $this->assertIdentical($config->get('non-existent', 'default'), 'default');
+    // A call to get with no key should still return an array() as NULL default
+    // will not be used.
+    $this->assertIdentical($config->get(), array());
+
     // Create a new configuration object.
     $config->set('value', 'initial');
     $config->save();