diff --git a/core/core.services.yml b/core/core.services.yml
index 60673fa..3da23c7 100644
--- a/core/core.services.yml
+++ b/core/core.services.yml
@@ -143,7 +143,7 @@ services:
   cache.backend.memory:
     class: Drupal\Core\Cache\MemoryBackendFactory
     arguments: ['@cache_tags.invalidator.checksum']
-  # A special cache bin that by default does not persist beyond the length of the request.
+  # A special cache bin that does not persist beyond the length of the request.
   cache.static:
     class: Drupal\Core\Cache\CacheBackendInterface
     tags:
diff --git a/core/lib/Drupal/Core/Session/PermissionsHashGenerator.php b/core/lib/Drupal/Core/Session/PermissionsHashGenerator.php
index 5c79d04..19178ba 100644
--- a/core/lib/Drupal/Core/Session/PermissionsHashGenerator.php
+++ b/core/lib/Drupal/Core/Session/PermissionsHashGenerator.php
@@ -45,7 +45,9 @@ class PermissionsHashGenerator implements PermissionsHashGeneratorInterface {
    * @param \Drupal\Core\PrivateKey $private_key
    *   The private key service.
    * @param \Drupal\Core\Cache\CacheBackendInterface $cache
-   *   The cache backend interface to use for the permission hash cache.
+   *   The cache backend interface to use for the persistent cache.
+   * @param \Drupal\Core\Cache\CacheBackendInterface
+   *   The cache backend interface to use for the static cache.
    */
   public function __construct(PrivateKey $private_key, CacheBackendInterface $cache, CacheBackendInterface $static) {
     $this->privateKey = $private_key;
@@ -62,19 +64,19 @@ public function generate(AccountInterface $account) {
     $sorted_roles = $account->getRoles();
     sort($sorted_roles);
     $role_list = implode(',', $sorted_roles);
-    $cid = "user_permissions_hasn:$role_list";
+    $cid = "user_permissions_hash:$role_list";
     if ($static_cache = $this->static->get($cid)) {
       return $static_cache->data;
     }
     else {
       $tags = Cache::buildTags('config:user.role', $sorted_roles, '.');
-      if ($cache = $this->cache->get("user_permissions_hash:$role_list")) {
+      if ($cache = $this->cache->get($cid)) {
         $permissions_hash = $cache->data;
         $this->static->set($cid, $permissions_hash, Cache::PERMANENT, $tags);
       }
       else {
         $permissions_hash = $this->doGenerate($sorted_roles);
-        $this->cache->set("user_permissions_hash:$role_list", $permissions_hash, Cache::PERMANENT, $tags);
+        $this->cache->set($cid, $permissions_hash, Cache::PERMANENT, $tags);
       }
     }
 
diff --git a/core/tests/Drupal/Tests/Core/Session/PermissionsHashTest.php b/core/tests/Drupal/Tests/Core/Session/PermissionsHashTest.php
index d760daa..8ba99b4 100644
--- a/core/tests/Drupal/Tests/Core/Session/PermissionsHashTest.php
+++ b/core/tests/Drupal/Tests/Core/Session/PermissionsHashTest.php
@@ -55,6 +55,13 @@ class PermissionsHashTest extends UnitTestCase {
   protected $cache;
 
   /**
+   * The mocked cache backend.
+   *
+   * @var \Drupal\Core\Cache\CacheBackendInterface|\PHPUnit_Framework_MockObject_MockObject
+   */
+  protected $staticCache;
+
+  /**
    * The permission hash class being tested.
    *
    * @var \Drupal\Core\Session\PermissionsHashGeneratorInterface
@@ -111,12 +118,15 @@ protected function setUp() {
     $this->cache = $this->getMockBuilder('Drupal\Core\Cache\CacheBackendInterface')
       ->disableOriginalConstructor()
       ->getMock();
+    $this->staticCache = $this->getMockBuilder('Drupal\Core\Cache\CacheBackendInterface')
+      ->disableOriginalConstructor()
+      ->getMock();
 
-    $this->permissionsHash = new PermissionsHashGenerator($this->privateKey, $this->cache, new \Drupal\Core\Cache\MemoryBackend('test'));
+    $this->permissionsHash = new PermissionsHashGenerator($this->privateKey, $this->cache, $this->staticCache);
   }
 
   /**
-   * Tests the generate() method.
+   * @covers ::generate
    */
   public function testGenerate() {
     // Ensure that two user accounts with the same roles generate the same hash.
@@ -130,15 +140,20 @@ public function testGenerate() {
   }
 
   /**
-   * Tests the generate method with persistent cache returned.
+   * @covers ::generate
    */
   public function testGeneratePersistentCache() {
     // Set expectations for the mocked cache backend.
     $expected_cid = 'user_permissions_hash:administrator,authenticated';
-
     $mock_cache = new \stdClass();
     $mock_cache->data = 'test_hash_here';
-
+    $this->staticCache->expects($this->once())
+      ->method('get')
+      ->with($expected_cid)
+      ->will($this->returnValue(FALSE));
+    $this->staticCache->expects($this->once())
+      ->method('set')
+      ->with($expected_cid, $this->isType('string'));
     $this->cache->expects($this->once())
       ->method('get')
       ->with($expected_cid)
@@ -150,20 +165,22 @@ public function testGeneratePersistentCache() {
   }
 
   /**
-   * Tests the generate method with static cache returned.
+   * @covers ::generate
    */
   public function testGenerateStaticCache() {
     // Set expectations for the mocked cache backend.
     $expected_cid = 'user_permissions_hash:administrator,authenticated';
-
     $mock_cache = new \stdClass();
     $mock_cache->data = 'test_hash_here';
-
-    $this->permissionsHasn = new PermissionsHashGenerator($this->privateKey, new \Drupal\Core\Cache\MemoryBackend('test'), $this->cache);
-    $this->cache->expects($this->once())
+    $this->staticCache->expects($this->once())
       ->method('get')
       ->with($expected_cid)
       ->will($this->returnValue($mock_cache));
+    $this->staticCache->expects($this->never())
+      ->method('set');
+
+    $this->cache->expects($this->never())
+      ->method('get');
     $this->cache->expects($this->never())
       ->method('set');
 
@@ -177,6 +194,13 @@ public function testGenerateNoCache() {
     // Set expectations for the mocked cache backend.
     $expected_cid = 'user_permissions_hash:administrator,authenticated';
 
+    $this->staticCache->expects($this->once())
+      ->method('get')
+      ->with($expected_cid)
+      ->will($this->returnValue(FALSE));
+    $this->staticCache->expects($this->once())
+      ->method('set')
+      ->with($expected_cid, $this->isType('string'));
     $this->cache->expects($this->once())
       ->method('get')
       ->with($expected_cid)
diff --git a/sites/development.services.yml b/sites/development.services.yml
index cc21211..73cc998 100644
--- a/sites/development.services.yml
+++ b/sites/development.services.yml
@@ -3,7 +3,5 @@
 # To activate this feature, follow the instructions at the top of the
 # 'example.settings.local.php' file, which sits next to this file.
 services:
-  cache.backend.memory:
-    class: Drupal\Core\Cache\MemoryBackendFactory
   cache.backend.null:
     class: Drupal\Core\Cache\NullBackendFactory