diff --git a/core/lib/Drupal/Core/EventSubscriber/DefaultExceptionSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/DefaultExceptionSubscriber.php
index e0a1343..2ed5176 100644
--- a/core/lib/Drupal/Core/EventSubscriber/DefaultExceptionSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/DefaultExceptionSubscriber.php
@@ -159,7 +159,7 @@ protected function onJson(GetResponseForExceptionEvent $event) {
     // of message to be displayed,
     $data = NULL;
     if (error_displayable($error) && $message = $exception->getMessage()) {
-      $data = ['error' => sprintf('A fatal error occurred: %s', $message)];
+      $data = ['message' => sprintf('A fatal error occurred: %s', $message)];
     }
 
     $response = new JsonResponse($data, Response::HTTP_INTERNAL_SERVER_ERROR);
diff --git a/core/modules/rest/src/Tests/AuthTest.php b/core/modules/rest/src/Tests/AuthTest.php
index 09537c8..c222b26 100644
--- a/core/modules/rest/src/Tests/AuthTest.php
+++ b/core/modules/rest/src/Tests/AuthTest.php
@@ -40,7 +40,7 @@ public function testRead() {
     // Try to read the resource as an anonymous user, which should not work.
     $this->httpRequest($entity->urlInfo(), 'GET', NULL, $this->defaultMimeType);
     $this->assertResponse('401', 'HTTP response code is 401 when the request is not authenticated and the user is anonymous.');
-    $this->assertRaw(json_encode(['error' => 'A fatal error occurred: No authentication credentials provided.']));
+    $this->assertRaw(json_encode(['message' => 'A fatal error occurred: No authentication credentials provided.']));
 
     // Ensure that cURL settings/headers aren't carried over to next request.
     unset($this->curlHandle);
diff --git a/core/modules/rest/src/Tests/ReadTest.php b/core/modules/rest/src/Tests/ReadTest.php
index d5f2fc1..7cac1f9 100644
--- a/core/modules/rest/src/Tests/ReadTest.php
+++ b/core/modules/rest/src/Tests/ReadTest.php
@@ -61,7 +61,7 @@ public function testRead() {
       $response = $this->httpRequest($entity_type . '/9999', 'GET', NULL, $this->defaultMimeType);
       $this->assertResponse(404);
       $path = $entity_type == 'node' ? '/node/{node}' : '/entity_test/{entity_test}';
-      $expected_message = Json::encode(['error' => 'A fatal error occurred: The "' . $entity_type . '" parameter was not converted for the path "' . $path . '" (route name: "rest.entity.' . $entity_type . '.GET.hal_json")']);
+      $expected_message = Json::encode(['message' => 'A fatal error occurred: The "' . $entity_type . '" parameter was not converted for the path "' . $path . '" (route name: "rest.entity.' . $entity_type . '.GET.hal_json")']);
       $this->assertIdentical($expected_message, $response, 'Response message is correct.');
 
       // Make sure that field level access works and that the according field is