diff -u b/core/modules/serialization/src/Normalizer/EntityValidationExceptionNormalizer.php b/core/modules/serialization/src/Normalizer/EntityValidationExceptionNormalizer.php
--- b/core/modules/serialization/src/Normalizer/EntityValidationExceptionNormalizer.php
+++ b/core/modules/serialization/src/Normalizer/EntityValidationExceptionNormalizer.php
@@ -22,7 +22,7 @@
   public function normalize($object, $format = NULL, array $context = []) {
     $result = [];
 
-    if ($object instanceof $this->supportedInterfaceOrClass) {
+    if ($this->supportsNormalization($object, $format)) {
       $result['message'] = $object->getMessage();
 
       // Group violations by field path.