.../src/Plugin/rest/resource/EntityResource.php    |  2 +-
 .../EntityResource/EntityResourceTestBase.php      | 31 ++++++++++++++++++++--
 2 files changed, 30 insertions(+), 3 deletions(-)

diff --git a/core/modules/rest/src/Plugin/rest/resource/EntityResource.php b/core/modules/rest/src/Plugin/rest/resource/EntityResource.php
index 1d61994..b4352b7 100644
--- a/core/modules/rest/src/Plugin/rest/resource/EntityResource.php
+++ b/core/modules/rest/src/Plugin/rest/resource/EntityResource.php
@@ -232,7 +232,7 @@ public function patch(EntityInterface $original_entity, EntityInterface $entity
       $field = $entity->get($field_name);
       $original_field = $original_entity->get($field_name);
 
-      // Check access for all received fields, but only if the are being
+      // Check access for all received fields, but only if they are being
       // changed. The bundle of an entity, for example, must be provided for
       // denormalization to succeed, but it may not be changed.
       if (!$original_field->equals($field) && !$original_field->access('edit')) {
diff --git a/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php b/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
index adde7a6..c8240d2 100644
--- a/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
+++ b/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
@@ -3,13 +3,17 @@
 namespace Drupal\Tests\rest\Functional\EntityResource;
 
 use Drupal\Component\Utility\NestedArray;
+use Drupal\Component\Utility\Random;
 use Drupal\Core\Cache\Cache;
 use Drupal\Core\Cache\CacheableResponseInterface;
 use Drupal\Core\Config\Entity\ConfigEntityInterface;
 use Drupal\Core\Entity\FieldableEntityInterface;
+use Drupal\Core\Field\Plugin\Field\FieldType\BooleanItem;
+use Drupal\Core\Field\Plugin\Field\FieldType\EntityReferenceItem;
 use Drupal\Core\Url;
 use Drupal\field\Entity\FieldConfig;
 use Drupal\field\Entity\FieldStorageConfig;
+use Drupal\path\Plugin\Field\FieldType\PathItem;
 use Drupal\rest\ResourceResponseInterface;
 use Drupal\Tests\rest\Functional\ResourceTestBase;
 use GuzzleHttp\RequestOptions;
@@ -1026,8 +1030,31 @@ public function testPatch() {
     $original_values = [];
     foreach (static::$patchProtectedFieldNames as $field_name) {
       $field = $modified_entity->get($field_name);
-      $original_values[$field_name] = $field->value;
-      $field->generateSampleItems();
+      $original_values[$field_name] = $field->getValue();
+      switch ($field->getItemDefinition()->getClass()) {
+        case EntityReferenceItem::class:
+          // EntityReferenceItem::generateSampleValue() picks one of the last 50
+          // entities of the supported type & bundle. We don't care if the value
+          // is valid, we only care that it's different.
+          $field->setValue(['target_id' => 99999]);
+          break;
+        case BooleanItem::class:
+          // BooleanItem::generateSampleValue() picks either 0 or 1. So a 50%
+          // chance of not picking a different value.
+          $field->value = ((int) $field->value) === 1 ? '0' : '1';
+          break;
+        case PathItem::class:
+          // PathItem::generateSampleValue() doesn't set a PID, which causes
+          // PathItem::postSave() to fail. Keep the PID (and other properties),
+          // just modify the alias.
+          $value = $field->getValue();
+          $value['alias'] = str_replace(' ', '-', strtolower((new Random())->sentences(3)));
+          $field->setValue($value);
+          break;
+        default:
+          $field->generateSampleItems();
+          break;
+      }
     }
     // Send PATCH request by serializing the cloned entity, assert the error
     // response, change the cloned entity field that caused the error response