diff --git a/core/lib/Drupal/Core/KeyValueStore/KeyValueStoreInterface.php b/core/lib/Drupal/Core/KeyValueStore/KeyValueStoreInterface.php
index 372ffc519e37c4fa8031955848382b2d479330a6..60c150cb10d7710cc059f947017f19e66bee6a80 100644
--- a/core/lib/Drupal/Core/KeyValueStore/KeyValueStoreInterface.php
+++ b/core/lib/Drupal/Core/KeyValueStore/KeyValueStoreInterface.php
@@ -25,11 +25,13 @@ public function getCollectionName();
    *
    * @param string $key
    *   The key of the data to retrieve.
+   * @param mixed $default
+   *   The default value to use if the key is not found.
    *
    * @return mixed
-   *   The stored value, or NULL if no value exists.
+   *   The stored value, or the default value if no value exists.
    */
-  public function get($key);
+  public function get($key, $default = NULL);
 
   /**
    * Returns the stored key/value pairs for a given set of keys.
diff --git a/core/lib/Drupal/Core/KeyValueStore/MemoryStorage.php b/core/lib/Drupal/Core/KeyValueStore/MemoryStorage.php
index 236b0aadab422e1b05e7e31f67f5ef3e67aaccda..e6e07ef7cb4ce9a522dd081953be5128db83c432 100644
--- a/core/lib/Drupal/Core/KeyValueStore/MemoryStorage.php
+++ b/core/lib/Drupal/Core/KeyValueStore/MemoryStorage.php
@@ -22,8 +22,8 @@ class MemoryStorage extends StorageBase {
   /**
    * Implements Drupal\Core\KeyValueStore\KeyValueStoreInterface::get().
    */
-  public function get($key) {
-    return array_key_exists($key, $this->data) ? $this->data[$key] : NULL;
+  public function get($key, $default = NULL) {
+    return array_key_exists($key, $this->data) ? $this->data[$key] : $default;
   }
 
   /**
diff --git a/core/lib/Drupal/Core/KeyValueStore/NullStorageExpirable.php b/core/lib/Drupal/Core/KeyValueStore/NullStorageExpirable.php
index d66ab597b7953f0299686d6ba256b1be4ce7656a..29bcde67999cb4eceb99ae68639c72c98b1b2273 100644
--- a/core/lib/Drupal/Core/KeyValueStore/NullStorageExpirable.php
+++ b/core/lib/Drupal/Core/KeyValueStore/NullStorageExpirable.php
@@ -36,7 +36,7 @@ public function __construct($collection) {
   /**
    * Implements Drupal\Core\KeyValueStore\KeyValueStoreInterface::get().
    */
-  public function get($key) {
+  public function get($key, $default = NULL) {
     return NULL;
   }
 
diff --git a/core/lib/Drupal/Core/KeyValueStore/StorageBase.php b/core/lib/Drupal/Core/KeyValueStore/StorageBase.php
index 6b643983e95b0c53fad8961ac30c609359cd4e25..4c54271f0a3ea64c36a204ca758bb52fb8dd4d42 100644
--- a/core/lib/Drupal/Core/KeyValueStore/StorageBase.php
+++ b/core/lib/Drupal/Core/KeyValueStore/StorageBase.php
@@ -36,9 +36,9 @@ public function getCollectionName() {
   /**
    * Implements Drupal\Core\KeyValueStore\KeyValueStoreInterface::get().
    */
-  public function get($key) {
+  public function get($key, $default = NULL) {
     $values = $this->getMultiple(array($key));
-    return isset($values[$key]) ? $values[$key] : NULL;
+    return isset($values[$key]) ? $values[$key] : $default;
   }
 
   /**
diff --git a/core/modules/system/lib/Drupal/system/Tests/KeyValueStore/StorageTestBase.php b/core/modules/system/lib/Drupal/system/Tests/KeyValueStore/StorageTestBase.php
index 6ae1a86251bf76b6e2d804cceea4be846efce9d4..86e6ce82b257c90c24a65047e919d3d545beeecf 100644
--- a/core/modules/system/lib/Drupal/system/Tests/KeyValueStore/StorageTestBase.php
+++ b/core/modules/system/lib/Drupal/system/Tests/KeyValueStore/StorageTestBase.php
@@ -157,6 +157,9 @@ public function testNonExistingKeys() {
     // Verify that a non-existing key returns NULL as value.
     $this->assertNull($stores[0]->get('foo'));
 
+    // Verify that a non-existing key with a default returns the default.
+    $this->assertIdentical($stores[0]->get('foo', 'bar'), 'bar');
+
     // Verify that a FALSE value can be stored.
     $stores[0]->set('foo', FALSE);
     $this->assertIdentical($stores[0]->get('foo'), FALSE);