diff -u b/core/modules/field/field.api.php b/core/modules/field/field.api.php
--- b/core/modules/field/field.api.php
+++ b/core/modules/field/field.api.php
@@ -729,8 +729,9 @@
  *   arguments received by hook_field_widget_form():
  *   - form: The form structure to which widgets are being attached. This may be
  *     a full form structure, or a sub-element of a larger form.
- *   - field: The field structure.
- *   - instance: The field instance structure.
+ *   - field_definition: The field definition.
+ *   - entity_type: The entity type.
+ *   - bundle: The entity bundle.
  *   - langcode: The language associated with $items.
  *   - items: Array of default values for this field.
  *   - delta: The order of this item in the array of subelements (0, 1, 2, etc).
@@ -764,9 +765,9 @@
  *   arguments received by hook_field_widget_form():
  *   - "form": The form structure where widgets are being attached to. This
  *     might be a full form structure, or a sub-element of a larger form.
- *   - "field": The field structure.
- *   - "instance": The field instance structure.
- *   - "langcode": The language associated with $items.
+ *   - "field_definition": The field definition.
+ *   - "entity_type": The entity type.
+ *   - "bundle": The entity bundle.
  *   - "items": Array of default values for this field.
  *   - "delta": The order of this item in the array of subelements (0, 1, 2,
  *     etc).
diff -u b/core/modules/field/lib/Drupal/field/Plugin/Type/Widget/WidgetBase.php b/core/modules/field/lib/Drupal/field/Plugin/Type/Widget/WidgetBase.php
--- b/core/modules/field/lib/Drupal/field/Plugin/Type/Widget/WidgetBase.php
+++ b/core/modules/field/lib/Drupal/field/Plugin/Type/Widget/WidgetBase.php
@@ -273,6 +273,8 @@
       $context = array(
         'form' => $form,
         'field_definition' => $this->field_definition,
+        'entity_type' => $entity->entityType(),
+        'bundle' => $entity->bundle(),
         'langcode' => $langcode,
         'items' => $items,
         'delta' => $delta,
diff -u b/core/modules/field/tests/modules/field_test/field_test.module b/core/modules/field/tests/modules/field_test/field_test.module
--- b/core/modules/field/tests/modules/field_test/field_test.module
+++ b/core/modules/field/tests/modules/field_test/field_test.module
@@ -226,12 +226,12 @@
   $field_name = $context['field_definition']['field_name'];
   switch ($field_name) {
     case 'alter_test_text':
-      $instance = field_info_instance($element['value']['#entity_type'], $field_name, $element['value']['#bundle']);
+      $instance = field_info_instance($context['entity_type'], $field_name, $context['bundle']);
       drupal_set_message('Field size: ' . $instance->getWidget()->getSetting('size'));
       break;
 
     case 'alter_test_options':
-      $instance = field_info_instance($element['value']['#entity_type'], $field_name, $element['value']['#bundle']);
+      $instance = field_info_instance($context['entity_type'], $field_name, $context['bundle']);
       drupal_set_message('Widget type: ' . $instance->getWidget()->getPluginId());
       break;
   }