.../serialization/src/Normalizer/NormalizerBase.php       | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/core/modules/serialization/src/Normalizer/NormalizerBase.php b/core/modules/serialization/src/Normalizer/NormalizerBase.php
index 4215fb3..37fde6d 100644
--- a/core/modules/serialization/src/Normalizer/NormalizerBase.php
+++ b/core/modules/serialization/src/Normalizer/NormalizerBase.php
@@ -3,8 +3,10 @@
 namespace Drupal\serialization\Normalizer;
 
 use Drupal\Core\Cache\CacheableDependencyInterface;
+use Drupal\Core\Field\EntityReferenceFieldItemListInterface;
 use Drupal\Core\Field\FieldItemInterface;
 use Drupal\Core\Field\FieldItemListInterface;
+use Drupal\Core\Field\Plugin\Field\FieldType\EntityReferenceItem;
 use Drupal\field_normalization_test\Normalization\TextItemSillyNormalizer;
 use Drupal\hal\Normalizer\FieldNormalizer as HalFieldNormalizer;
 use Drupal\hal\Normalizer\FieldItemNormalizer as HalFieldItemNormalizer;
@@ -123,9 +125,6 @@ protected static function disallowFieldLevelNormalizers(array $supported, $norma
       FieldItemNormalizer::class,
       HalFieldNormalizer::class,
       HalFieldItemNormalizer::class,
-      // Entity reference field normalizers for both normalizations.
-      EntityReferenceFieldItemNormalizer::class,
-      HalEntityReferenceItemNormalizer::class,
       // The NULL normalizer allows one to prevent listed classes from ever
       // being normalized. By default, this is applied only to the 'password'
       // field type.
@@ -137,14 +136,20 @@ protected static function disallowFieldLevelNormalizers(array $supported, $norma
       HalTimestampItemNormalizer::class,
     ];
 
-    $is_disallowed = function ($name) {
+    $is_field_class = function ($name) {
       return in_array($name, [FieldItemInterface::class, FieldItemListInterface::class], TRUE)
         || is_subclass_of($name, FieldItemInterface::class, TRUE)
         || is_subclass_of($name, FieldItemListInterface::class, TRUE);
     };
 
+    $is_entity_reference_field_class = function ($name) {
+      return in_array($name, [EntityReferenceItem::class, EntityReferenceFieldItemListInterface::class], TRUE)
+        || is_subclass_of($name, EntityReferenceItem::class, TRUE)
+        || is_subclass_of($name, EntityReferenceFieldItemListInterface::class, TRUE);
+    };
+
     foreach ($supported as $name) {
-      if (!in_array($normalizer_class, $allowed_exceptions, TRUE) && $is_disallowed($name)) {
+      if (!in_array($normalizer_class, $allowed_exceptions, TRUE) && !$is_entity_reference_field_class($name) && $is_field_class($name)) {
         @trigger_error(sprintf('%s is a normalizer for a @FieldType plugin. This is very strongly discouraged because it requires similar logic to be implemented for every normalization. Please write this as a normalizer for a @DataType plugin instead, then it works for the entire Drupal API-First ecosystem!', $normalizer_class), E_USER_DEPRECATED);
       }
     }