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 e4485e0..f456400 100644
--- a/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/EntityReferenceItem.php
+++ b/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/EntityReferenceItem.php
@@ -13,8 +13,8 @@
 use Drupal\Core\Field\FieldDefinitionInterface;
 use Drupal\Core\Field\FieldItemBase;
 use Drupal\Core\Field\FieldStorageDefinitionInterface;
-use Drupal\Core\TypedData\DataDefinition;
 use Drupal\Core\TypedData\DataReferenceDefinition;
+use Drupal\Core\TypedData\DataReferenceTargetDefinition;
 
 /**
  * Defines the 'entity_reference' entity field type.
@@ -74,12 +74,12 @@ public static function propertyDefinitions(FieldStorageDefinitionInterface $fiel
     }
 
     if ($target_id_data_type === 'integer') {
-      $target_id_definition = DataDefinition::create('integer')
+      $target_id_definition = DataReferenceTargetDefinition::create('integer')
         ->setLabel(t('@label ID', array($target_type_info->getLabel())))
         ->setSetting('unsigned', TRUE);
     }
     else {
-      $target_id_definition = DataDefinition::create('string')
+      $target_id_definition = DataReferenceTargetDefinition::create('string')
         ->setLabel(t('@label ID', array($target_type_info->getLabel())));
     }
     $target_id_definition->setRequired(TRUE);
diff --git a/core/lib/Drupal/Core/TypedData/DataReferenceTargetDefinition.php b/core/lib/Drupal/Core/TypedData/DataReferenceTargetDefinition.php
new file mode 100644
index 0000000..4c5d9a4
--- /dev/null
+++ b/core/lib/Drupal/Core/TypedData/DataReferenceTargetDefinition.php
@@ -0,0 +1,27 @@
+<?php
+/**
+ * @file
+ * Contains DataReferenceTargetDefinition.php
+ */
+
+namespace Drupal\Core\TypedData;
+
+
+class DataReferenceTargetDefinition extends DataDefinition {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getConstraints() {
+    $constraints = parent::getConstraints();
+    // If this data definition is marked as required for the sake of schema
+    // definitions, we don't enforce it using the NotNull constraint. Instead
+    // \Drupal\Core\Field\EntityReferenceFieldItemList::getConstraints() adds
+    // the 'EntityReferenceNotNull' constraint that operates at the field-item
+    // list level.
+    unset($constraints['NotNull']);
+    return $constraints;
+  }
+
+
+}