diff --git a/core/modules/datetime_range/src/DateTimeRangeTrait.php b/core/modules/datetime_range/src/DateTimeRangeTrait.php
index daeca49..5a34f2c 100644
--- a/core/modules/datetime_range/src/DateTimeRangeTrait.php
+++ b/core/modules/datetime_range/src/DateTimeRangeTrait.php
@@ -2,6 +2,7 @@
 
 namespace Drupal\datetime_range;
 
+use Drupal\Core\Datetime\DrupalDateTime;
 use Drupal\datetime\Plugin\Field\FieldType\DateTimeItem;
 
 /**
@@ -18,15 +19,21 @@
    * @return array
    *   A render array.
    */
-  protected function buildDate($date) {
+  protected function buildDate(DrupalDateTime $date) {
     if ($this->getFieldSetting('datetime_type') == DateTimeItem::DATETIME_TYPE_DATE) {
       // A date without time will pick up the current time, use the default.
       datetime_date_default_time($date);
     }
     $this->setTimeZone($date);
 
-    $build = ['#plain_text' => $this->formatDate($date)];
-    $build['#cache']['contexts'][] = 'timezone';
+    $build = [
+      '#plain_text' => $this->formatDate($date),
+      '#cache' => [
+        'contexts' => [
+          'timezone',
+        ],
+      ],
+    ];
 
     return $build;
   }
@@ -40,7 +47,7 @@ protected function buildDate($date) {
    * @return array
    *   A render array.
    */
-  protected function buildDateWithIsoAttribute($date) {
+  protected function buildDateWithIsoAttribute(DrupalDateTime $date) {
     if ($this->getFieldSetting('datetime_type') == DateTimeItem::DATETIME_TYPE_DATE) {
       // A date without time will pick up the current time, use the default.
       datetime_date_default_time($date);
@@ -58,8 +65,12 @@ protected function buildDateWithIsoAttribute($date) {
       '#attributes' => [
         'datetime' => $iso_date,
       ],
+      '#cache' => [
+        'contexts' => [
+          'timezone',
+        ],
+      ],
     ];
-    $build['#cache']['contexts'][] = 'timezone';
 
     return $build;
   }
diff --git a/core/modules/datetime_range/src/Plugin/Field/FieldWidget/DateRangeWidgetBase.php b/core/modules/datetime_range/src/Plugin/Field/FieldWidget/DateRangeWidgetBase.php
index 5e695b3..ae9f24a 100644
--- a/core/modules/datetime_range/src/Plugin/Field/FieldWidget/DateRangeWidgetBase.php
+++ b/core/modules/datetime_range/src/Plugin/Field/FieldWidget/DateRangeWidgetBase.php
@@ -124,7 +124,7 @@ public function massageFormValues(array $values, array $form, FormStateInterface
    * @param array $complete_form
    *   The complete form structure.
    */
-  public function validateStartEnd(&$element, FormStateInterface $form_state, &$complete_form) {
+  public function validateStartEnd(array &$element, FormStateInterface $form_state, array &$complete_form) {
     $start_date = $element['value']['#value']['object'];
     $end_date = $element['end_value']['#value']['object'];