diff --git a/core/lib/Drupal/Core/Entity/EntityForm.php b/core/lib/Drupal/Core/Entity/EntityForm.php
index 43b5da36ab..017239e46d 100644
--- a/core/lib/Drupal/Core/Entity/EntityForm.php
+++ b/core/lib/Drupal/Core/Entity/EntityForm.php
@@ -217,10 +217,12 @@ protected function synchronizeEntityBetweenGetAndPostRequests(FormStateInterface
           break;
         case 'POST':
           $user_input = $form_state->getUserInput();
-          $this->entitySyncHashKey = $user_input['entity_sync_hash_key'];
-          $entity = $key_value_store->get($this->entitySyncHashKey);
-          $entity = unserialize($entity);
-          $this->entity = $entity;
+          if (isset($user_input['entity_sync_hash_key'])) {
+            $this->entitySyncHashKey = $user_input['entity_sync_hash_key'];
+            $entity = $key_value_store->get($this->entitySyncHashKey);
+            $entity = unserialize($entity);
+            $this->entity = $entity;
+          }
           break;
       }
     }
@@ -239,10 +241,12 @@ public function form(array $form, FormStateInterface $form_state) {
 
     // The entity sync hash key must be sent to the client, in order to be able
     // to load the entity used to build the form in later form requests.
-    $form['entity_sync_hash_key'] = [
-      '#type' => 'hidden',
-      '#default_value' => $this->entitySyncHashKey,
-    ];
+    if (isset($this->entitySyncHashKey)) {
+      $form['entity_sync_hash_key'] = [
+        '#type' => 'hidden',
+        '#default_value' => $this->entitySyncHashKey,
+      ];
+    }
 
     return $form;
   }