diff -u b/core/modules/field_ui/src/Form/FieldStorageAddForm.php b/core/modules/field_ui/src/Form/FieldStorageAddForm.php
--- b/core/modules/field_ui/src/Form/FieldStorageAddForm.php
+++ b/core/modules/field_ui/src/Form/FieldStorageAddForm.php
@@ -114,6 +114,7 @@
     $form['add'] = [
       '#type' => 'container',
       '#attributes' => ['class' => ['form--inline', 'clearfix']],
+      '#weight' => -10,
     ];
 
     $form['add']['new_storage_type'] = [
@@ -140,7 +141,8 @@
         '#empty_option' => $this->t('- Select an existing field -'),
       ];
 
-      $form['#attached']['drupalSettings']['existingFieldLabels'] = $this->getExistingFieldLabels(array_keys($existing_field_storage_options));
+      $existing_field_labels = $this->getExistingFieldLabels(array_keys($existing_field_storage_options));
+      $form['#attached']['drupalSettings']['existingFieldLabels'] = $existing_field_labels;
     }
     else {
       // Provide a placeholder form element to simplify the validation code.
@@ -150,22 +152,41 @@
       ];
     }
 
-    // New field storage subform wrapper.
+    $form['add']['rebuild'] = [
+      '#type' => 'submit',
+      '#value' => $this->t('Update'),
+      '#attributes' => ['class' => ['js-hide'], 'style' => ['margin-top: 2.2em']],
+      '#limit_validation_errors' => [],
+      '#submit' => ['::newStorageTypeSubmit'],
+    ];
+
+    $user_input = $form_state->getUserInput();
+
+    $existing_storage_name = isset($user_input['existing_storage_name']) ? $user_input['existing_storage_name'] : '';
+    if ($existing_storage_name) {
+      // Field label and field_name.
+      $form['label'] = [
+        '#type' => 'value',
+        '#value' => $existing_field_labels[$existing_storage_name],
+      ];
+    }
+
     $form['new_storage_wrapper'] = [
       '#type' => 'container',
       '#id' => 'new-storage-wrapper',
     ];
-
-    if ($form_state->isRebuilding() && ($new_storage_type = $form_state->getValue('new_storage_type'))) {
+    $new_storage_type = isset($user_input['new_storage_type']) ? $user_input['new_storage_type'] : '';
+    if ($new_storage_type) {
+      // New field storage subform wrapper.
+      $field_prefix = $this->config('field_ui.settings')->get('field_prefix');
       // Field label and field_name.
       $form['new_storage_wrapper']['label'] = [
         '#type' => 'textfield',
         '#title' => $this->t('Label'),
         '#size' => 15,
+        '#required' => TRUE,
         '#weight' => -15,
       ];
-
-      $field_prefix = $this->config('field_ui.settings')->get('field_prefix');
       $form['new_storage_wrapper']['field_name'] = [
         '#type' => 'machine_name',
         // This field should stay LTR even for RTL languages.
@@ -180,7 +201,7 @@
           'source' => ['new_storage_wrapper', 'label'],
           'exists' => [$this, 'fieldNameExists'],
         ],
-        '#required' => FALSE,
+        '#required' => TRUE,
         '#weight' => -14,
       ];
 
@@ -227,18 +248,2 @@
 
-    // Provide a separate label element for the "Re-use existing field" case
-    // and place it outside the $form['add'] wrapper because those elements
-    // are displayed inline.
-    if ($existing_field_storage_options) {
-      $form['existing_storage_label'] = [
-        '#type' => 'textfield',
-        '#title' => $this->t('Label'),
-        '#size' => 15,
-        '#states' => [
-          '!visible' => [
-            ':input[name="existing_storage_name"]' => ['value' => ''],
-          ],
-        ],
-      ];
-    }
-
     // Place the 'translatable' property as an explicit value so that contrib
@@ -294,7 +299,6 @@
     }
 
     $this->validateAddNew($form, $form_state);
-    $this->validateAddExisting($form, $form_state);
   }
 
   /**
@@ -338,19 +341,0 @@
-  /**
-   * Validates the 're-use existing field' case.
-   *
-   * @param array $form
-   *   An associative array containing the structure of the form.
-   * @param \Drupal\Core\Form\FormStateInterface $form_state
-   *   The current state of the form.
-   *
-   * @see \Drupal\field_ui\Form\FieldStorageAddForm::validateForm()
-   */
-  protected function validateAddExisting(array $form, FormStateInterface $form_state) {
-    if ($form_state->getValue('existing_storage_name')) {
-      // Missing label.
-      if (!$form_state->getValue('existing_storage_label')) {
-        $form_state->setErrorByName('existing_storage_label', $this->t('Re-use existing field: you need to provide a label.'));
-      }
-    }
-  }
-
@@ -414,12 +399,15 @@
       $field_name = $values['existing_storage_name'];
 
       try {
-        $field = $this->entityManager->getStorage('field_config')->create([
+        $definition = [
           'field_name' => $field_name,
           'entity_type' => $this->entityTypeId,
           'bundle' => $this->bundle,
-          'label' => $values['existing_storage_label'],
-        ]);
+        ];
+        if ($values['label'] != 'undefined') {
+          $definition['label'] = $values['label'];
+        }
+        $field = $this->entityManager->getStorage('field_config')->create($definition);
         $field->save();
 
         $this->configureEntityFormDisplay($field_name);
only in patch2:
unchanged:
--- a/core/modules/field_ui/field_ui.es6.js
+++ b/core/modules/field_ui/field_ui.es6.js
@@ -16,26 +16,11 @@
         .find('[data-drupal-selector="field-ui-field-storage-add-form"]')
         .once('field_ui_add');
       if ($form.length) {
-        // Add a few 'js-form-required' and 'form-required' css classes here.
-        // We can not use the Form API '#required' property because both label
-        // elements for "add new" and "re-use existing" can never be filled and
-        // submitted at the same time. The actual validation will happen
-        // server-side.
-        $form
-          .find(
-            '.js-form-item-label label,' +
-              '.js-form-item-field-name label,' +
-              '.js-form-item-existing-storage-label label',
-          )
-          .addClass('js-form-required form-required');
-
         const $newFieldType = $form.find('select[name="new_storage_type"]');
+        const $newFieldName = $form.find('input[name="field_name"]');
         const $existingStorageName = $form.find(
           'select[name="existing_storage_name"]',
         );
-        const $existingStorageLabel = $form.find(
-          'input[name="existing_storage_label"]',
-        );
 
         // When the user selects a new field type, clear the "existing field"
         // selection.
@@ -47,21 +32,13 @@
         });
 
         // When the user selects an existing storage name, clear the "new field
-        // type" selection and populate the 'existing_storage_label' element.
+        // type" selection.
         $existingStorageName.on('change', function() {
           const value = $(this).val();
           if (value !== '') {
             // Reset the "new field type" selection.
             $newFieldType.val('').trigger('change');
-
-            // Pre-populate the "existing storage label" element.
-            if (
-              typeof drupalSettings.existingFieldLabels[value] !== 'undefined'
-            ) {
-              $existingStorageLabel.val(
-                drupalSettings.existingFieldLabels[value],
-              );
-            }
+            $newFieldName.val('').trigger('change');
           }
         });
       }
only in patch2:
unchanged:
--- a/core/modules/field_ui/field_ui.js
+++ b/core/modules/field_ui/field_ui.js
@@ -10,11 +10,9 @@
     attach: function attach(context) {
       var $form = $(context).find('[data-drupal-selector="field-ui-field-storage-add-form"]').once('field_ui_add');
       if ($form.length) {
-        $form.find('.js-form-item-label label,' + '.js-form-item-field-name label,' + '.js-form-item-existing-storage-label label').addClass('js-form-required form-required');
-
         var $newFieldType = $form.find('select[name="new_storage_type"]');
+        var $newFieldName = $form.find('input[name="field_name"]');
         var $existingStorageName = $form.find('select[name="existing_storage_name"]');
-        var $existingStorageLabel = $form.find('input[name="existing_storage_label"]');
 
         $newFieldType.on('change', function () {
           if ($(this).val() !== '') {
@@ -26,10 +24,7 @@
           var value = $(this).val();
           if (value !== '') {
             $newFieldType.val('').trigger('change');
-
-            if (typeof drupalSettings.existingFieldLabels[value] !== 'undefined') {
-              $existingStorageLabel.val(drupalSettings.existingFieldLabels[value]);
-            }
+            $newFieldName.val('').trigger('change');
           }
         });
       }