core/modules/rest/src/Plugin/rest/resource/EntityResource.php | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/core/modules/rest/src/Plugin/rest/resource/EntityResource.php b/core/modules/rest/src/Plugin/rest/resource/EntityResource.php
index 6428cbb..0477982 100644
--- a/core/modules/rest/src/Plugin/rest/resource/EntityResource.php
+++ b/core/modules/rest/src/Plugin/rest/resource/EntityResource.php
@@ -148,8 +148,9 @@ public function patch(EntityInterface $original_entity, EntityInterface $entity
     $bundle_key = $entity->getEntityType()->getKey('bundle');
     foreach ($entity->_restSubmittedFields as $field_name) {
       // \Drupal\serialization\Normalizer\EntityNormalizer::denormalize() needs
-      // the bundle to be able to denormalize the entity.
-      if ($field_name === $bundle_key) {
+      // the bundle to be able to denormalize the entity, if the entity type has
+      // a bundle key.
+      if ($bundle_key && $field_name === $bundle_key) {
         continue;
       }