core/modules/rest/src/Plugin/rest/resource/EntityResource.php | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/core/modules/rest/src/Plugin/rest/resource/EntityResource.php b/core/modules/rest/src/Plugin/rest/resource/EntityResource.php
index d15e993..72f5c52 100644
--- a/core/modules/rest/src/Plugin/rest/resource/EntityResource.php
+++ b/core/modules/rest/src/Plugin/rest/resource/EntityResource.php
@@ -155,7 +155,10 @@ public function patch(EntityInterface $original_entity, EntityInterface $entity
     foreach ($entity->_restSubmittedFields as $field_name) {
       $field = $entity->get($field_name);
 
-      // Entity key fields need special treatment.
+      // Entity key fields need special treatment: together they uniquely
+      // identify the entity. Therefore it does not make sense to modify any of
+      // them. However, rather than throwing an error, we just ignore them as
+      // long as their specified values match their current values.
       if (in_array($field_name, $entity_keys)) {
         // Unchanged Values for entity keys same don't need access checking.
         if ($original_entity->get($field_name)->getValue() === $entity->get($field_name)->getValue()) {