.../Normalizer/DateTimeIso8601Normalizer.php           |  7 ++++++-
 .../Normalizer/DateTimeNormalizer.php                  | 18 +++++-------------
 2 files changed, 11 insertions(+), 14 deletions(-)

diff --git a/src/ForwardCompatibility/Normalizer/DateTimeIso8601Normalizer.php b/src/ForwardCompatibility/Normalizer/DateTimeIso8601Normalizer.php
index 6fde623..ac07bb9 100644
--- a/src/ForwardCompatibility/Normalizer/DateTimeIso8601Normalizer.php
+++ b/src/ForwardCompatibility/Normalizer/DateTimeIso8601Normalizer.php
@@ -2,6 +2,7 @@
 
 namespace Drupal\jsonapi\ForwardCompatibility\Normalizer;
 
+use Drupal\Core\Datetime\DrupalDateTime;
 use Drupal\Core\TypedData\Plugin\DataType\DateTimeIso8601;
 use Drupal\datetime\Plugin\Field\FieldType\DateTimeItem;
 
@@ -37,7 +38,11 @@ class DateTimeIso8601Normalizer extends DateTimeNormalizer {
   public function normalize($datetime, $format = NULL, array $context = []) {
     $field_item = $datetime->getParent();
     if ($field_item instanceof DateTimeItem && $field_item->getFieldDefinition()->getFieldStorageDefinition()->getSetting('datetime_type') === DateTimeItem::DATETIME_TYPE_DATE) {
-      return $this->getDateTime($datetime)->format($this->allowedFormats['date-only']);
+      // @todo Remove when JSON:API only supports Drupal >=8.7, which fixed this in https://www.drupal.org/project/drupal/issues/3002164.
+      $drupal_date_time = floatval(floatval(\Drupal::VERSION) >= 8.7)
+        ? $datetime->getDateTime()
+        : new DrupalDateTime($datetime->getValue(), 'UTC');
+      return $drupal_date_time->format($this->allowedFormats['date-only']);
     }
     return parent::normalize($datetime, $format, $context);
   }
diff --git a/src/ForwardCompatibility/Normalizer/DateTimeNormalizer.php b/src/ForwardCompatibility/Normalizer/DateTimeNormalizer.php
index fa4dd09..12e4911 100644
--- a/src/ForwardCompatibility/Normalizer/DateTimeNormalizer.php
+++ b/src/ForwardCompatibility/Normalizer/DateTimeNormalizer.php
@@ -41,7 +41,11 @@ class DateTimeNormalizer extends NormalizerBase implements DenormalizerInterface
    * {@inheritdoc}
    */
   public function normalize($datetime, $format = NULL, array $context = []) {
-    return $this->getDateTime($datetime)
+    // @todo Remove when JSON:API only supports Drupal >=8.7, which fixed this in https://www.drupal.org/project/drupal/issues/3002164.
+    $drupal_date_time = floatval(floatval(\Drupal::VERSION) >= 8.7)
+      ? $datetime->getDateTime()
+      : new DrupalDateTime($datetime->getValue(), 'UTC');
+    return $drupal_date_time
       // Set an explicit timezone. Otherwise, timestamps may end up being
       // normalized using the user's preferred timezone. Which would result in
       // many variations and complex caching.
@@ -52,18 +56,6 @@ class DateTimeNormalizer extends NormalizerBase implements DenormalizerInterface
   }
 
   /**
-   * Returns the date time object after observing source timezone is UTC.
-   *
-   * @see \Drupal\Core\TypedData\Plugin\DataType\DateTimeIso8601::getDateTime()
-   *
-   * @return \Drupal\Core\Datetime\DrupalDateTime
-   *   A date object.
-   */
-  protected function getDateTime($datetime) {
-    return new DrupalDateTime($datetime->getValue(), 'UTC');
-  }
-
-  /**
    * Gets the timezone to be used during normalization.
    *
    * @see ::normalize