diff --git a/core/lib/Drupal/Core/Field/WidgetBase.php b/core/lib/Drupal/Core/Field/WidgetBase.php
index 8fa66fd39a..87451b69ef 100644
--- a/core/lib/Drupal/Core/Field/WidgetBase.php
+++ b/core/lib/Drupal/Core/Field/WidgetBase.php
@@ -248,16 +248,16 @@ protected function formMultipleElements(FieldItemListInterface $items, array &$f
           'form' => $form,
           'widget' => $this,
           'items' => $items,
-          'delta' => $delta,
           'default' => $this->isDefaultValueWidget($form_state),
+          'cardinality' => $cardinality,
         ];
         \Drupal::moduleHandler()->alter([
           'field_widget_multiple_form',
           'field_widget_multiple_' . $this->getPluginId() . '_form',
         ], $elements, $form_state, $context);
       }
-
     }
+
     return $elements;
   }
 
@@ -326,12 +326,14 @@ public static function addMoreAjax(array $form, FormStateInterface $form_state)
    * Generates the form element for a single copy of the widget.
    */
   protected function formSingleElement(FieldItemListInterface $items, $delta, array $element, array &$form, FormStateInterface $form_state) {
+    $cardinality = $this->fieldDefinition->->getFieldStorageDefinition()->getCardinality();
     $element += [
       '#field_parents' => $form['#parents'],
       // Only the first widget should be required.
       '#required' => $delta == 0 && $this->fieldDefinition->isRequired(),
       '#delta' => $delta,
       '#weight' => $delta,
+      '#cardinality' => $cardinality,
     ];
 
     $element = $this->formElement($items, $delta, $element, $form, $form_state);
@@ -344,6 +346,7 @@ protected function formSingleElement(FieldItemListInterface $items, $delta, arra
         'items' => $items,
         'delta' => $delta,
         'default' => $this->isDefaultValueWidget($form_state),
+        'cardinality' => $cardinality,
       ];
       \Drupal::moduleHandler()->alter(['field_widget_form', 'field_widget_' . $this->getPluginId() . '_form'], $element, $form_state, $context);
     }
diff --git a/core/modules/field/field.api.php b/core/modules/field/field.api.php
index 1fd8427e8c..d9708db87c 100644
--- a/core/modules/field/field.api.php
+++ b/core/modules/field/field.api.php
@@ -179,6 +179,8 @@ function hook_field_widget_info_alter(array &$info) {
  *   - delta: The order of this item in the array of subelements (0, 1, 2, etc).
  *   - default: A boolean indicating whether the form is being shown as a dummy
  *     form to set default values.
+ *   - cardinality: The cardinality of the field in the field storage. See
+ *     \Drupal\Core\Field\FieldStorageDefinitionInterface for possible values.
  *
  * @see \Drupal\Core\Field\WidgetBaseInterface::form()
  * @see \Drupal\Core\Field\WidgetBase::formSingleElement()
@@ -240,12 +242,13 @@ function hook_field_widget_WIDGET_TYPE_form_alter(&$element, \Drupal\Core\Form\F
  *   - widget: The widget plugin instance.
  *   - items: The field values, as a
  *     \Drupal\Core\Field\FieldItemListInterface object.
- *   - delta: The order of this item in the array of subelements (0, 1, 2, etc).
  *   - default: A boolean indicating whether the form is being shown as a dummy
  *     form to set default values.
+ *   - cardinality: The cardinality of the field in the field storage. See
+ *     \Drupal\Core\Field\FieldStorageDefinitionInterface for possible values.
  *
  * @see \Drupal\Core\Field\WidgetBaseInterface::form()
- * @see \Drupal\Core\Field\WidgetBase::formSingleElement()
+ * @see \Drupal\Core\Field\WidgetBase::formMultipleElements()
  * @see hook_field_widget_form_alter()
  * @see hook_field_widget_multiple_WIDGET_TYPE_form_alter()
  */
@@ -274,7 +277,7 @@ function hook_field_widget_multiple_form_alter(array &$elements, \Drupal\Core\Fo
  *   and content of the array.
  *
  * @see \Drupal\Core\Field\WidgetBaseInterface::form()
- * @see \Drupal\Core\Field\WidgetBase::formSingleElement()
+ * @see \Drupal\Core\Field\WidgetBase::formMultipleElements()
  * @see hook_field_widget_multiple_form_alter()
  */
 function hook_field_widget_multiple_WIDGET_TYPE_form_alter(array &$elements, \Drupal\Core\Form\FormStateInterface $form_state, array $context) {