diff -u b/core/lib/Drupal/Core/Field/WidgetBase.php b/core/lib/Drupal/Core/Field/WidgetBase.php
--- b/core/lib/Drupal/Core/Field/WidgetBase.php
+++ b/core/lib/Drupal/Core/Field/WidgetBase.php
@@ -148,7 +148,7 @@
     switch ($cardinality) {
       case FieldStorageDefinitionInterface::CARDINALITY_UNLIMITED:
         $field_state = static::getWidgetState($parents, $field_name, $form_state);
-        $max = $field_state['items_count'];
+        $max = $field_state['items_count'] - 1;
         $is_multiple = TRUE;
         break;
 
@@ -163,7 +163,7 @@
 
     $elements = [];
 
-    for ($delta = 0; $delta < $max; $delta++) {
+    for ($delta = 0; $delta <= $max; $delta++) {
       // Add a new empty item if it doesn't exist yet at this delta.
       if (!isset($items[$delta])) {
         $items->appendItem();
@@ -208,68 +208,66 @@
       }
     }
 
-    if ($elements) {
-      $elements += [
-        '#theme' => 'field_multiple_value_form',
-        '#field_name' => $field_name,
-        '#cardinality' => $cardinality,
-        '#cardinality_multiple' => $this->fieldDefinition->getFieldStorageDefinition()->isMultiple(),
-        '#required' => $this->fieldDefinition->isRequired(),
-        '#title' => $title,
-        '#description' => $description,
-        '#max_delta' => $max,
-      ];
+    $elements += [
+      '#theme' => 'field_multiple_value_form',
+      '#field_name' => $field_name,
+      '#cardinality' => $cardinality,
+      '#cardinality_multiple' => $this->fieldDefinition->getFieldStorageDefinition()->isMultiple(),
+      '#required' => $this->fieldDefinition->isRequired(),
+      '#title' => $title,
+      '#description' => $description,
+      '#max_delta' => $max,
+    ];
+
+    // Add 'add more' button, if not working with a programmed form.
+    if ($cardinality == FieldStorageDefinitionInterface::CARDINALITY_UNLIMITED && !$form_state->isProgrammed()) {
+      $id_prefix = implode('-', array_merge($parents, [$field_name]));
+      $wrapper_id = Html::getUniqueId($id_prefix . '-add-more-wrapper');
+      $form['#wrapper_id'] = $wrapper_id;
+      $elements['#prefix'] = '<div id="' . $wrapper_id . '">';
+      $elements['#suffix'] = '</div>';
 
-      // Add 'add more' button, if not working with a programmed form.
-      if ($cardinality == FieldStorageDefinitionInterface::CARDINALITY_UNLIMITED && !$form_state->isProgrammed()) {
-        $id_prefix = implode('-', array_merge($parents, [$field_name]));
-        $wrapper_id = Html::getUniqueId($id_prefix . '-add-more-wrapper');
-        $form['#wrapper_id'] = $wrapper_id;
-        $elements['#prefix'] = '<div id="' . $wrapper_id . '">';
+      foreach ($elements as $element) {
+        $elements['#prefix'] = '<div id="' . $form['#wrapper_id'] . '">';
         $elements['#suffix'] = '</div>';
+        $elements['add_more']['#ajax']['wrapper'] = $form['#wrapper_id'];
+      }
 
-        foreach ($elements as $element) {
-          $elements['#prefix'] = '<div id="' . $form['#wrapper_id'] . '">';
-          $elements['#suffix'] = '</div>';
-          $elements['add_more']['#ajax']['wrapper'] = $form['#wrapper_id'];
-        }
-
-        $elements['add_more'] = [
-          '#type' => 'submit',
-          '#name' => strtr($id_prefix, '-', '_') . '_add_more',
-          '#value' => t('Add another item'),
-          '#attributes' => ['class' => ['field-add-more-submit']],
-          '#limit_validation_errors' => [array_merge($parents, [$field_name])],
-          '#submit' => [[get_class($this), 'addMoreSubmit']],
-          '#ajax' => [
-            'callback' => [get_class($this), 'addMoreAjax'],
-            'wrapper' => $wrapper_id,
-            'effect' => 'fade',
-          ],
-        ];
+      $elements['add_more'] = [
+        '#type' => 'submit',
+        '#name' => strtr($id_prefix, '-', '_') . '_add_more',
+        '#value' => t('Add another item'),
+        '#attributes' => ['class' => ['field-add-more-submit']],
+        '#limit_validation_errors' => [array_merge($parents, [$field_name])],
+        '#submit' => [[get_class($this), 'addMoreSubmit']],
+        '#ajax' => [
+          'callback' => [get_class($this), 'addMoreAjax'],
+          'wrapper' => $wrapper_id,
+          'effect' => 'fade',
+        ],
+      ];
 
-        for ($delta = 0; $delta < $max; $delta++) {
-          $elements[$delta]['actions'] = [
-            '#type' => 'actions',
-            'remove_button' => [
-              '#delta' => $delta,
-              '#name' => implode('_', array_merge($elements[$delta]['#field_parents'], [$field_name, $delta])) . '_remove_button',
-              '#type' => 'submit',
-              '#value' => t('Remove'),
-              '#validate' => [],
-              '#submit' => [[$this, 'ajaxSubmitRemove']],
-              '#limit_validation_errors' => [],
-              '#attributes' => [
-                'class' => ['remove-field-delta--' . $delta],
-              ],
-              '#ajax' => [
-                'callback' => [$this, 'removeAjaxContentRefresh'],
-                'effect' => 'fade',
-                'wrapper' => $form['#wrapper_id'],
-              ],
+      for ($delta = 0; $delta <= $max; $delta++) {
+        $elements[$delta]['actions'] = [
+          '#type' => 'actions',
+          'remove_button' => [
+            '#delta' => $delta,
+            '#name' => implode('_', array_merge($elements[$delta]['#field_parents'], [$field_name, $delta])) . '_remove_button',
+            '#type' => 'submit',
+            '#value' => t('Remove'),
+            '#validate' => [],
+            '#submit' => [[$this, 'ajaxSubmitRemove']],
+            '#limit_validation_errors' => [],
+            '#attributes' => [
+              'class' => ['remove-field-delta--' . $delta],
             ],
-          ];
-        }
+            '#ajax' => [
+              'callback' => [$this, 'removeAjaxContentRefresh'],
+              'effect' => 'fade',
+              'wrapper' => $form['#wrapper_id'],
+            ],
+          ],
+        ];
       }
     }
 
@@ -342,7 +340,7 @@
    *
    * This re-numbers form elements and removes an item.
    */
-  public function ajaxSubmitRemove($form, FormStateInterface $form_state) {
+  public function ajaxSubmitRemove(&$form, FormStateInterface $form_state) {
     $button = $form_state->getTriggeringElement();
     $delta = $button['#delta'];
     $array_parents = array_slice($button['#array_parents'], 0, -4);
@@ -352,30 +350,29 @@
     $parents = $parent_element['#field_parents'];
     $field_state = static::getWidgetState($parents, $field_name, $form_state);
     for ($i = $delta; $i < $field_state['items_count']; $i++) {
-      $old_element_widget = array_merge($array_parents, ['widget', $i + 1]);
-      $old_element = array_merge($old_parents, [$i + 1]);
-      $new_element = array_merge($old_parents, [$i]);
-      $moving_element = NestedArray::getValue($form, $old_element_widget);
-      $moving_element_value = NestedArray::getValue($form_state->getValues(), $old_element);
-      $moving_element_input = NestedArray::getValue($form_state->getUserInput(), $old_element);
+      $old_element_widget_parents = array_merge($array_parents, ['widget', $i + 1]);
+      $old_element_parents = array_merge($old_parents, [$i + 1]);
+      $new_element_parents = array_merge($old_parents, [$i]);
+      $moving_element = NestedArray::getValue($form, $old_element_widget_parents);
+      $moving_element_input = NestedArray::getValue($form_state->getUserInput(), $old_element_parents);
 
       // Tell the element where it's being moved to.
-      $moving_element['#parents'] = $new_element;
+      $moving_element['#parents'] = $new_element_parents;
 
       // Move the element around.
-      $form_state->setValueForElement($moving_element, $moving_element_value);
       $user_input = $form_state->getUserInput();
       NestedArray::setValue($user_input, $moving_element['#parents'], $moving_element_input);
       $user_input[$field_name] = array_filter($user_input[$field_name]);
       $form_state->setUserInput($user_input);
     }
+    unset($parent_element[$delta]);
+    NestedArray::setValue($form, $array_parents, $parent_element);
 
-    $weight_multiplier = 1;
     if ($field_state['items_count'] > 0) {
-      $weight_multiplier = $field_state['items_count'] - 1;
+      $field_state['items_count']--;
     }
     $input = NestedArray::getValue($form_state->getUserInput(), $array_parents);
-    $weight = -1 * $weight_multiplier;
+    $weight = -1 * $field_state['items_count'];
     foreach ($input as $key => $item) {
       if ($item) {
         $input[$key]['_weight'] = $weight++;
@@ -384,9 +381,8 @@
     $user_input = $form_state->getUserInput();
     NestedArray::setValue($user_input, $array_parents, $input);
     $form_state->setUserInput($user_input);
-
     static::setWidgetState($parents, $field_name, $form_state, $field_state);
-
+    $form_state->setRebuild();
   }
 
   /**
@@ -397,7 +393,7 @@
    */
   public function removeAjaxContentRefresh(array &$form, FormStateInterface $form_state) {
     $button = $form_state->getTriggeringElement();
-    return NestedArray::getValue($form, array_slice($button['#array_parents'], 0, -3));
+    return NestedArray::getValue($form, array_slice($button['#array_parents'], 0, -4));
   }
 
   /**