src/Normalizer/EntityNormalizer.php | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/src/Normalizer/EntityNormalizer.php b/src/Normalizer/EntityNormalizer.php
index b436669..f2cd5c0 100644
--- a/src/Normalizer/EntityNormalizer.php
+++ b/src/Normalizer/EntityNormalizer.php
@@ -184,7 +184,13 @@ class EntityNormalizer extends NormalizerBase implements DenormalizerInterface {
    */
   protected function getFields($entity, $bundle, ResourceType $resource_type) {
     $output = [];
-    $fields = TypedDataInternalPropertiesHelper::getNonInternalProperties($entity->getTypedData());
+    // @todo Remove this when JSON API requires Drupal 8.5 or newer.
+    if (floatval(\Drupal::VERSION) >= 8.5) {
+      $fields = TypedDataInternalPropertiesHelper::getNonInternalProperties($entity->getTypedData());
+    }
+    else {
+      $fields = $entity->getFields();
+    }
     // Filter the array based on the field names.
     $enabled_field_names = array_filter(
       array_keys($fields),