.../Functional/EntityResource/EntityTest/EntityTestDateonlyTest.php    | 2 +-
 core/modules/serialization/src/Normalizer/DateTimeNormalizer.php       | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/core/modules/datetime/tests/src/Functional/EntityResource/EntityTest/EntityTestDateonlyTest.php b/core/modules/datetime/tests/src/Functional/EntityResource/EntityTest/EntityTestDateonlyTest.php
index d7a8043..e8c71ef 100644
--- a/core/modules/datetime/tests/src/Functional/EntityResource/EntityTest/EntityTestDateonlyTest.php
+++ b/core/modules/datetime/tests/src/Functional/EntityResource/EntityTest/EntityTestDateonlyTest.php
@@ -146,7 +146,7 @@ protected function assertNormalizationEdgeCases($method, Url $url, array $reques
 
       $request_options[RequestOptions::BODY] = $this->serializer->encode($normalization, static::$format);
       $response = $this->request($method, $url, $request_options);
-      $message = "Unprocessable Entity: validation failed.\n{$fieldName}.0: The datetime value '{$value}' did not parse properly for the format 'Y-m-d'\n{$fieldName}.0.value: This value should be of the correct primitive type.\n";
+      $message = "The specified date \"$value\" is not in an accepted format: \"Y-m-d\" (date-only).";
       $this->assertResourceErrorResponse(422, $message, $response);
     }
   }
diff --git a/core/modules/serialization/src/Normalizer/DateTimeNormalizer.php b/core/modules/serialization/src/Normalizer/DateTimeNormalizer.php
index e0a72a9..3435af6 100644
--- a/core/modules/serialization/src/Normalizer/DateTimeNormalizer.php
+++ b/core/modules/serialization/src/Normalizer/DateTimeNormalizer.php
@@ -83,7 +83,8 @@ public function denormalize($data, $class, $format = NULL, array $context = [])
       : $this->allowedFormats;
     foreach ($allowed_formats as $format) {
       $date = \DateTime::createFromFormat($format, $data);
-      if ($date !== FALSE) {
+      $errors = \DateTime::getLastErrors();
+      if ($date !== FALSE && empty($errors['errors']) && empty($errors['warnings'])) {
         return $date;
       }
     }