.../Functional/EntityResource/EntityTest/EntityTestDateonlyTest.php   | 2 +-
 .../Functional/EntityResource/EntityTest/EntityTestDatetimeTest.php   | 4 ++--
 2 files changed, 3 insertions(+), 3 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 0fb404d..d7a8043 100644
--- a/core/modules/datetime/tests/src/Functional/EntityResource/EntityTest/EntityTestDateonlyTest.php
+++ b/core/modules/datetime/tests/src/Functional/EntityResource/EntityTest/EntityTestDateonlyTest.php
@@ -136,7 +136,7 @@ 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}' is invalid for the format 'Y-m-d'\n";
+      $message = "The specified date \"$value\" is not in an accepted format: \"Y-m-d\" (date-only).";
       $this->assertResourceErrorResponse(422, $message, $response);
 
       // DX: 422 when value is not a valid date.
diff --git a/core/modules/datetime/tests/src/Functional/EntityResource/EntityTest/EntityTestDatetimeTest.php b/core/modules/datetime/tests/src/Functional/EntityResource/EntityTest/EntityTestDatetimeTest.php
index ef0010e..a37f20d 100644
--- a/core/modules/datetime/tests/src/Functional/EntityResource/EntityTest/EntityTestDatetimeTest.php
+++ b/core/modules/datetime/tests/src/Functional/EntityResource/EntityTest/EntityTestDatetimeTest.php
@@ -136,7 +136,7 @@ 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}' is invalid for the format 'Y-m-d\\TH:i:s'\n";
+      $message = "The specified date \"$value\" is not in an accepted format: \"Y-m-d\\TH:i:sP\" (RFC 3339), \"Y-m-d\\TH:i:sO\" (ISO 8601).";
       $this->assertResourceErrorResponse(422, $message, $response);
 
       // DX: 422 when date format is incorrect.
@@ -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 '{$value}' did not parse properly for the format 'Y-m-d\\TH:i:s'\n{$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\\TH:i:sP\" (RFC 3339), \"Y-m-d\\TH:i:sO\" (ISO 8601).";
       $this->assertResourceErrorResponse(422, $message, $response);
     }
   }