diff --git a/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
index f7ab2d7..aa21673 100644
--- a/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -1898,8 +1898,8 @@ function drupal_get_user_timezone() {
   global $user;
   $config = config('system.timezone');
 
-  if ($user && $config->get('user.configurable') && $user->id() && $user->timezone) {
-    return $user->timezone;
+  if ($user && $config->get('user.configurable') && $user->id() && $user->getTimezone()) {
+    return $user->getTimezone();
   }
   else {
     // Ignore PHP strict notice if time zone has not yet been set in the php.ini
diff --git a/core/includes/session.inc b/core/includes/session.inc
index ae37211..049d46e 100644
--- a/core/includes/session.inc
+++ b/core/includes/session.inc
@@ -122,14 +122,14 @@ function _drupal_session_read($sid) {
     // The user is anonymous or blocked. Only preserve two fields from the
     // {sessions} table.
     $account = drupal_anonymous_user();
-    $account->session = $user->session;
-    $account->timestamp = $user->timestamp;
+    $account->setSessionData($user->getSessionData());
+    $account->setLastAccessedTime($user->getLastAccessedTime());
     $user = $account;
   }
   else {
     // The session has expired.
     $user = drupal_anonymous_user();
-    $user->session = '';
+    $user->setSessionData(array());
   }
 
   // Store the session that was read for comparison in _drupal_session_write().
diff --git a/core/lib/Drupal/Core/Session/AccountInterface.php b/core/lib/Drupal/Core/Session/AccountInterface.php
index 62420a2..c57b6eb 100644
--- a/core/lib/Drupal/Core/Session/AccountInterface.php
+++ b/core/lib/Drupal/Core/Session/AccountInterface.php
@@ -132,4 +132,12 @@ public function getEmail();
    */
   public function getLastAccessedTime();
 
+  /**
+   * Returns the timezone of the user.
+   *
+   * @return string
+   *   Name of the timezone.
+   */
+  public function getTimeZone();
+
 }
diff --git a/core/lib/Drupal/Core/Session/UserSession.php b/core/lib/Drupal/Core/Session/UserSession.php
index 0745db1..bc64e51 100644
--- a/core/lib/Drupal/Core/Session/UserSession.php
+++ b/core/lib/Drupal/Core/Session/UserSession.php
@@ -94,6 +94,13 @@ class UserSession implements AccountInterface {
   protected $mail;
 
   /**
+   * The timezone of this account.
+   *
+   * @var string
+   */
+  protected $timezone;
+
+  /**
    * Constructs a new user session.
    *
    * @param array $values
@@ -203,5 +210,32 @@ public function getLastAccessedTime() {
     return $this->timestamp;
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function getTimeZone() {
+    return $this->timezone;
+  }
+
+  /**
+   * Sets the last accessed time of this account.
+   *
+   * @param int $timestamp
+   *   The last accessed timestamp.
+   */
+  public function setLastAccessedTime($timestamp) {
+    $this->timestamp = $timestamp;
+  }
+
+  /**
+   * Sets current session.
+   *
+   * @param array $session
+   *   The session data.
+   */
+  public function setSessionData($session) {
+    $this->session = $session;
+  }
+
 
 }
diff --git a/core/modules/system/system.module b/core/modules/system/system.module
index 060f4db..280d529 100644
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -2427,7 +2427,7 @@ function system_user_presave(UserInterface $account) {
 function system_user_login($account) {
   $config = config('system.timezone');
   // If the user has a NULL time zone, notify them to set a time zone.
-  if (!$account->timezone && $config->get('user.configurable') && $config->get('user.warn')) {
+  if (!$account->getTimezone() && $config->get('user.configurable') && $config->get('user.warn')) {
     drupal_set_message(t('Configure your <a href="@user-edit">account time zone setting</a>.', array('@user-edit' => url("user/$account->id()/edit", array('query' => drupal_get_destination(), 'fragment' => 'edit-timezone')))));
   }
 }
@@ -2451,7 +2451,7 @@ function system_user_timezone(&$form, &$form_state) {
     '#options' => system_time_zones($account->id() != $user->id()),
     '#description' => t('Select the desired local time and time zone. Dates and times throughout this site will be displayed using this time zone.'),
   );
-  if (!isset($account->timezone) && $account->id() == $user->id() && empty($form_state['input']['timezone'])) {
+  if (!$account->getTimezone() && $account->id() == $user->id() && empty($form_state['input']['timezone'])) {
     $form['timezone']['#description'] = t('Your time zone setting will be automatically detected if possible. Confirm the selection and click save.');
     $form['timezone']['timezone']['#attributes'] = array('class' => array('timezone-detect'));
     drupal_add_library('system', 'drupal.timezone');
diff --git a/core/modules/user/lib/Drupal/user/Tests/UserRegistrationTest.php b/core/modules/user/lib/Drupal/user/Tests/UserRegistrationTest.php
index 7028261..f975664 100644
--- a/core/modules/user/lib/Drupal/user/Tests/UserRegistrationTest.php
+++ b/core/modules/user/lib/Drupal/user/Tests/UserRegistrationTest.php
@@ -184,7 +184,7 @@ function testRegistrationDefaultValues() {
     $this->assertEqual($new_user->getSignature(), '', 'Correct signature field.');
     $this->assertTrue(($new_user->getCreatedTime() > REQUEST_TIME - 20 ), 'Correct creation time.');
     $this->assertEqual($new_user->isActive(), $config_user_settings->get('register') == USER_REGISTER_VISITORS ? 1 : 0, 'Correct status field.');
-    $this->assertEqual($new_user->timezone->value, $config_system_timezone->get('default'), 'Correct time zone field.');
+    $this->assertEqual($new_user->getTimezone(), $config_system_timezone->get('default'), 'Correct time zone field.');
     $this->assertEqual($new_user->langcode->value, language_default()->id, 'Correct language field.');
     $this->assertEqual($new_user->preferred_langcode->value, language_default()->id, 'Correct preferred language field.');
     $this->assertEqual($new_user->init->value, $mail, 'Correct init field.');
diff --git a/core/modules/user/lib/Drupal/user/UserInterface.php b/core/modules/user/lib/Drupal/user/UserInterface.php
index 4a3950d..e0bf1f9 100644
--- a/core/modules/user/lib/Drupal/user/UserInterface.php
+++ b/core/modules/user/lib/Drupal/user/UserInterface.php
@@ -176,14 +176,6 @@ public function activate();
   public function block();
 
   /**
-   * Returns the timezone of the user.
-   *
-   * @return string
-   *   Name of the timezone.
-   */
-  public function getTimeZone();
-
-  /**
    * Returns the e-mail that was used when the user was registered.
    *
    * @return string
diff --git a/core/modules/user/user.api.php b/core/modules/user/user.api.php
index 9e9fcaf..2e8fb8d 100644
--- a/core/modules/user/user.api.php
+++ b/core/modules/user/user.api.php
@@ -286,7 +286,7 @@ function hook_user_update($account) {
 function hook_user_login($account) {
   $config = config('system.timezone');
   // If the user has a NULL time zone, notify them to set a time zone.
-  if (!$account->timezone && $config->get('user.configurable') && $config->get('user.warn')) {
+  if (!$account->getTimezone() && $config->get('user.configurable') && $config->get('user.warn')) {
     drupal_set_message(t('Configure your <a href="@user-edit">account time zone setting</a>.', array('@user-edit' => url("user/" . $account->id() . "/edit", array('query' => drupal_get_destination(), 'fragment' => 'edit-timezone')))));
   }
 }