diff --git a/core/modules/datetime/src/Plugin/Field/FieldFormatter/DateTimeCustomFormatter.php b/core/modules/datetime/src/Plugin/Field/FieldFormatter/DateTimeCustomFormatter.php
index 984423d..ca40045 100644
--- a/core/modules/datetime/src/Plugin/Field/FieldFormatter/DateTimeCustomFormatter.php
+++ b/core/modules/datetime/src/Plugin/Field/FieldFormatter/DateTimeCustomFormatter.php
@@ -54,7 +54,7 @@ public function viewElements(FieldItemListInterface $items, $langcode) {
    */
   protected function formatDate($date) {
     $format = $this->getSetting('date_format');
-    $timezone = $this->getSetting('timezone_override');
+    $timezone = $this->getSetting('timezone_override') ?: $date->getTimezone()->getName();
     return $this->dateFormatter->format($date->getTimestamp(), 'custom', $format, $timezone != '' ? $timezone : NULL);
   }
 
diff --git a/core/modules/datetime/src/Plugin/Field/FieldFormatter/DateTimePlainFormatter.php b/core/modules/datetime/src/Plugin/Field/FieldFormatter/DateTimePlainFormatter.php
index 7f0dee2..875d1de 100644
--- a/core/modules/datetime/src/Plugin/Field/FieldFormatter/DateTimePlainFormatter.php
+++ b/core/modules/datetime/src/Plugin/Field/FieldFormatter/DateTimePlainFormatter.php
@@ -41,7 +41,7 @@ public function viewElements(FieldItemListInterface $items, $langcode) {
    */
   protected function formatDate($date) {
     $format = $this->getFieldSetting('datetime_type') == DateTimeItem::DATETIME_TYPE_DATE ? DATETIME_DATE_STORAGE_FORMAT : DATETIME_DATETIME_STORAGE_FORMAT;
-    $timezone = $this->getSetting('timezone_override');
+    $timezone = $this->getSetting('timezone_override') ?: $date->getTimezone()->getName();
     return $this->dateFormatter->format($date->getTimestamp(), 'custom', $format, $timezone != '' ? $timezone : NULL);
   }
 
diff --git a/core/modules/datetime/src/Tests/DateTestBase.php b/core/modules/datetime/src/Tests/DateTestBase.php
index 81e7550..4065da0 100644
--- a/core/modules/datetime/src/Tests/DateTestBase.php
+++ b/core/modules/datetime/src/Tests/DateTestBase.php
@@ -178,6 +178,7 @@ protected function setSiteTimezone($timezone) {
       ->set('timezone.user.configurable', 0)
       ->set('timezone.default', $timezone)
       ->save();
+    drupal_flush_all_caches();
   }
 
 }