.../src/Plugin/rest/resource/EntityResourceValidationTrait.php   | 6 ++++--
 .../src/Functional/EntityResource/EntityResourceTestBase.php     | 9 ++++++---
 2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/core/modules/rest/src/Plugin/rest/resource/EntityResourceValidationTrait.php b/core/modules/rest/src/Plugin/rest/resource/EntityResourceValidationTrait.php
index 69f80d6..e24e757 100644
--- a/core/modules/rest/src/Plugin/rest/resource/EntityResourceValidationTrait.php
+++ b/core/modules/rest/src/Plugin/rest/resource/EntityResourceValidationTrait.php
@@ -21,8 +21,7 @@
    *   The entity to validate.
    * @param string[] $changed_fields
    *   (optional) An array of field names. If specified, filters the violations
-   *   list to include only this set of fields. Defaults to an empty array,
-   *   which means that all violations will be reported.
+   *   list to include only this set of fields.
    *
    * @throws \Symfony\Component\HttpKernel\Exception\UnprocessableEntityHttpException
    *   If validation errors are found.
@@ -41,6 +40,9 @@ protected function validate(EntityInterface $entity, array $changed_fields = [])
     // Filter violations by the changed fields. New entities only have changed
     // fields.
     if (!$entity->isNew()) {
+      if (empty($changed_fields)) {
+        throw new \LogicException("Saving an entity without changing any fields does not make sense.");
+      }
       $violations->filterByFields(array_diff(array_keys($entity->getFieldDefinitions()), $changed_fields));
     }
 
diff --git a/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php b/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
index f64fd70..e8a9c2a 100644
--- a/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
+++ b/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
@@ -1155,8 +1155,7 @@ public function testPatch() {
 
     if ($this->entity instanceof FieldableEntityInterface) {
       // Change the rest_test_validation field to prove that then its validation
-      // does run. In subsequent test assertions, it will not be modified, and
-      // then should not trigger validation errors.
+      // does run.
       $override = [
         'rest_test_validation' => [
           [
@@ -1175,12 +1174,16 @@ public function testPatch() {
       $this->entity->set('rest_test_validation', 'ALWAYS_FAIL');
       $this->entity->save();
 
-      // Information dislcosure prevented: when a malicious user correctly
+      // Information disclosure prevented: when a malicious user correctly
       // guesses the current invalid value of a field, ensure a 200 is not sent
       // because this would disclose to the attacker what the current value is.
+      // @see rest_test_entity_field_access()
       $response = $this->request('PATCH', $url, $request_options);
       $this->assertResourceErrorResponse(422, "Unprocessable Entity: validation failed.\nrest_test_validation: REST test validation failed\n", $response);
 
+      // All requests after the above one will not include this field (neither
+      // its current value nor any other), and therefore all subsequent test
+      // assertions should not trigger a validation error.
     }
 
     // 200 for well-formed PATCH request that sends all fields (even including