diff --git a/core/modules/datetime/src/Plugin/Field/FieldFormatter/DateTimeFormatterBase.php b/core/modules/datetime/src/Plugin/Field/FieldFormatter/DateTimeFormatterBase.php
index 31d7dc5..0695982 100644
--- a/core/modules/datetime/src/Plugin/Field/FieldFormatter/DateTimeFormatterBase.php
+++ b/core/modules/datetime/src/Plugin/Field/FieldFormatter/DateTimeFormatterBase.php
@@ -92,6 +92,9 @@ public static function defaultSettings() {
   public function settingsForm(array $form, FormStateInterface $form_state) {
     $form = parent::settingsForm($form, $form_state);
 
+    // @todo There should be a way to specify/change which timezone the date
+    // is displayed with (eg, for an event site that spans multiple timezones,
+    // transforming the time into the site/user's timezone may not make sense).
     $form['timezone_override'] = array(
       '#type' => 'select',
       '#title' => $this->t('Time zone override'),
diff --git a/core/modules/datetime/src/Plugin/Field/FieldType/DateTimeItem.php b/core/modules/datetime/src/Plugin/Field/FieldType/DateTimeItem.php
index b56fd84..6ae7595 100644
--- a/core/modules/datetime/src/Plugin/Field/FieldType/DateTimeItem.php
+++ b/core/modules/datetime/src/Plugin/Field/FieldType/DateTimeItem.php
@@ -57,7 +57,6 @@ public static function propertyDefinitions(FieldStorageDefinitionInterface $fiel
       ->setClass('\Drupal\datetime\DateTimeComputed')
       ->setSetting('date source', 'value');
 
-    // @todo Shouldn't this only be needed if `$field_definition->getSetting('timezone_handling') === TRUE`?
     $properties['timezone'] = DataDefinition::create('string')
       ->setLabel(t('Timezone'));
 
@@ -75,21 +74,17 @@ public static function schema(FieldStorageDefinitionInterface $field_definition)
           'type' => 'varchar',
           'length' => 20,
         ),
+        'timezone' => array(
+          'description' => 'The date timezone',
+          'type' => 'varchar',
+          'length' => 50,
+        ),
       ),
       'indexes' => array(
-        'value' => array('value'),
+        'value' => array('value', 'timezone'),
       ),
     );
 
-    // Store the timezone if timezone handling is per-date.
-    if ($field_definition->getSetting('timezone_handling') === 'date') {
-      $schema['columns']['timezone'] = array(
-        'description' => 'The date timezone',
-        'type' => 'varchar',
-        'length' => 50,
-      );
-    }
-
     return $schema;
   }
 
@@ -123,6 +118,15 @@ public function storageSettingsForm(array &$form, FormStateInterface $form_state
       ),
       '#default_value' => $this->getSetting('timezone_handling'),
       '#required' => TRUE,
+      '#states' => array(
+        'visible' => array(
+          ':input[name="settings[datetime_type]"]' => ['value' => static::DATETIME_TYPE_DATETIME],
+        ),
+        'disabled' => array(
+          ':input[name="settings[datetime_type]"]' => ['value' => static::DATETIME_TYPE_DATE],
+        ),
+      ),
+      '#disabled' => $has_data,
     );
 
     return $element;
diff --git a/core/modules/datetime/src/Plugin/Field/FieldWidget/DateTimeWidgetBase.php b/core/modules/datetime/src/Plugin/Field/FieldWidget/DateTimeWidgetBase.php
index 864a0d3..d382f04 100644
--- a/core/modules/datetime/src/Plugin/Field/FieldWidget/DateTimeWidgetBase.php
+++ b/core/modules/datetime/src/Plugin/Field/FieldWidget/DateTimeWidgetBase.php
@@ -30,20 +30,21 @@ public function formElement(FieldItemListInterface $items, $delta, array $elemen
       '#type' => 'datetime',
       '#default_value' => NULL,
       '#date_increment' => 1,
-      '#date_timezone' => drupal_get_user_timezone(),
+      '#date_timezone' => $items[$delta]->timezone ?: drupal_get_user_timezone(),
       '#required' => $element['#required'],
     );
 
     if ($this->getFieldSetting('timezone_handling') === 'date') {
       $element['timezone'] = array(
         '#type' => 'select',
-        '#options' => \DateTimeZone::listIdentifiers(),
+        '#options' => array_combine(\DateTimeZone::listIdentifiers(), \DateTimeZone::listIdentifiers()),
         // Default to user's timezone.
         '#default_value' => drupal_get_user_timezone(),
       );
     }
 
     if ($items[$delta]->date) {
+      /** @var \Drupal\Core\Datetime\DrupalDateTime $date */
       $date = $items[$delta]->date;
       // The date was created and verified during field_load(), so it is safe to
       // use without further inspection.
@@ -54,6 +55,7 @@ public function formElement(FieldItemListInterface $items, $delta, array $elemen
       }
       $date->setTimezone(new \DateTimeZone($element['value']['#date_timezone']));
       $element['value']['#default_value'] = $date;
+      $element['timezone']['#default_value'] = $date->format('e');
     }
 
     return $element;