diff --git a/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/EntityReferenceItem.php b/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/EntityReferenceItem.php
index f46780e..e4485e0 100644
--- a/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/EntityReferenceItem.php
+++ b/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/EntityReferenceItem.php
@@ -82,6 +82,7 @@ public static function propertyDefinitions(FieldStorageDefinitionInterface $fiel
       $target_id_definition = DataDefinition::create('string')
         ->setLabel(t('@label ID', array($target_type_info->getLabel())));
     }
+    $target_id_definition->setRequired(TRUE);
     $properties['target_id'] = $target_id_definition;
 
     $properties['entity'] = DataReferenceDefinition::create('entity')