diff --git a/core/modules/field_ui/field_ui.js b/core/modules/field_ui/field_ui.js
index 9acc98f..0839833 100644
--- a/core/modules/field_ui/field_ui.js
+++ b/core/modules/field_ui/field_ui.js
@@ -11,49 +11,41 @@
     attach: function (context) {
       var $newFieldType = $(context).find('select[name="new_field_type"]').once('new-field-type');
       var $existingStorageName = $(context).find('select[name="existing_storage_name"]').once('existing-storage-name');
-      var $fieldLabel = $(context).find('input[name="label"]');
-      var $machineName = $(context).find('.form-item-label .field-suffix');
-      var labelValue;
 
-      // When the user selects a new field type, clear the "existing field"
-      // selection and re-populate the label if we have something in the cache.
       if ($newFieldType.length) {
+        // Add the 'form-required' css class 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.
+        $(context).find('.form-item-label label').addClass('form-required');
+        $(context).find('.form-item-field-name label').addClass('form-required');
+
+        // When the user selects a new field type, clear the "existing field"
+        // selection.
         $newFieldType.change(function () {
           if ($(this).val() != '') {
+            // Reset the "existing storage name" selection.
             $existingStorageName.val('').change();
-
-            if (labelValue != null) {
-              $fieldLabel.val(labelValue).trigger('keyup');
-              $machineName.show();
-              labelValue = null;
-            }
           }
         });
       }
 
-      // When the user selects an existing field, clear the "new field type"
-      // selection and populate the 'label' element.
       if ($existingStorageName.length) {
-        $existingStorageName.change(function (event) {
-          if ($(this).val() != '') {
-            // Keep the current label value (if any) in a static cache so we can
-            // re-use it if the user decides to select a new field type again.
-            if ($newFieldType.val()) {
-              labelValue = $fieldLabel.val();
-            }
+        // Add the 'form-required' css class to the label of the form element.
+        // The actual validation will happen server-side.
+        $(context).find('.form-item-existing-storage-label label').addClass('form-required');
 
-            // Reset the field type selection.
-            $newFieldType.val('');
+        // When the user selects an existing storage name, clear the "new field
+        // type" selection and populate the 'existing_storage_label' element.
+        $existingStorageName.change(function () {
+          if ($(this).val() != '') {
+            // Reset the "new field type" selection.
+            $newFieldType.val('').change();
 
-            // Pre-populate the label and hide the machine name (field_name).
-            $fieldLabel.val(drupalSettings.existingFieldLabels[$(this).val()]);
-            $machineName.hide();
-          }
-          // Reset the auto-populated label value if this is a user-initiated
-          // event (i.e. changing the value of the "existing field" element).
-          else if (event.originalEvent !== undefined && labelValue == null) {
-            $fieldLabel.val('');
-            $machineName.show();
+            // Pre-populate the "existing storage label" element.
+            if (drupalSettings.existingFieldLabels[$(this).val()] !== undefined) {
+              $(context).find('input[name="existing_storage_label"]').val(drupalSettings.existingFieldLabels[$(this).val()]);
+            }
           }
         });
       }
diff --git a/core/modules/field_ui/src/Form/FieldStorageAddForm.php b/core/modules/field_ui/src/Form/FieldStorageAddForm.php
index 5a265a4..cc5c7e7 100644
--- a/core/modules/field_ui/src/Form/FieldStorageAddForm.php
+++ b/core/modules/field_ui/src/Form/FieldStorageAddForm.php
@@ -175,25 +175,22 @@ public function buildForm(array $form, FormStateInterface $form_state, $entity_t
     }
 
     // Field label and field_name.
-    $form['name_wrapper'] = array(
+    $form['add_storage_wrapper'] = array(
       '#type' => 'container',
       '#states' => array(
         '!visible' => array(
           ':input[name="new_field_type"]' => array('value' => ''),
-          ':input[name="existing_storage_name"]' => array('value' => ''),
         ),
       ),
     );
-
-    $form['name_wrapper']['label'] = array(
+    $form['add_storage_wrapper']['label'] = array(
       '#type' => 'textfield',
       '#title' => $this->t('Label'),
       '#size' => 15,
-      '#required' => TRUE,
     );
 
     $field_prefix = $this->config('field_ui.settings')->get('field_prefix');
-    $form['name_wrapper']['field_name'] = array(
+    $form['add_storage_wrapper']['field_name'] = array(
       '#type' => 'machine_name',
       // This field should stay LTR even for RTL languages.
       '#field_prefix' => '<span dir="ltr">' . $field_prefix,
@@ -204,12 +201,28 @@ public function buildForm(array $form, FormStateInterface $form_state, $entity_t
       // setting. Maximum length is 32.
       '#maxlength' => FieldStorageConfig::NAME_MAX_LENGTH - strlen($field_prefix),
       '#machine_name' => array(
-        'source' => array('name_wrapper', 'label'),
+        'source' => array('add_storage_wrapper', 'label'),
         'exists' => array($this, 'fieldNameExists'),
       ),
       '#required' => FALSE,
     );
 
+    // 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'] = array(
+        '#type' => 'textfield',
+        '#title' => $this->t('Label'),
+        '#size' => 15,
+        '#states' => array(
+          '!visible' => array(
+            ':input[name="existing_storage_name"]' => array('value' => ''),
+          ),
+        ),
+      );
+    }
+
     // Place the 'translatable' property as an explicit value so that
     // contrib modules can form_alter() the value for newly created fields.
     $form['translatable'] = array(
@@ -261,6 +274,11 @@ public function validateForm(array &$form, FormStateInterface $form_state) {
   protected function validateAddNew(array $form, FormStateInterface $form_state) {
     // Validate if any information was provided in the 'add new field' case.
     if ($form_state->getValue('new_field_type')) {
+      // Missing label.
+      if (!$form_state->getValue('label')) {
+        $form_state->setErrorByName('label', $this->t('Add new field: you need to provide a label.'));
+      }
+
       // Missing field name.
       if (!$form_state->getValue('field_name')) {
         $form_state->setErrorByName('field_name', $this->t('Add new field: you need to provide a machine name for the field.'));
@@ -271,7 +289,7 @@ protected function validateAddNew(array $form, FormStateInterface $form_state) {
 
         // Add the field prefix.
         $field_name = $this->configFactory->get('field_ui.settings')->get('field_prefix') . $field_name;
-        $form_state->setValueForElement($form['name_wrapper']['field_name'], $field_name);
+        $form_state->setValueForElement($form['add_storage_wrapper']['field_name'], $field_name);
       }
     }
   }
@@ -288,8 +306,10 @@ protected function validateAddNew(array $form, FormStateInterface $form_state) {
    */
   protected function validateAddExisting(array $form, FormStateInterface $form_state) {
     if ($form_state->getValue('existing_storage_name')) {
-      // Discard any value that might be set for the field name.
-      $form_state->setValueForElement($form['name_wrapper']['field_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.'));
+      }
     }
   }
 
@@ -352,7 +372,7 @@ public function submitForm(array &$form, FormStateInterface $form_state) {
           'field_name' => $field_name,
           'entity_type' => $this->entityTypeId,
           'bundle' => $this->bundle,
-          'label' => $values['label'],
+          'label' => $values['existing_storage_label'],
         ));
         $field->save();
 
diff --git a/core/modules/field_ui/src/Tests/FieldUiTestTrait.php b/core/modules/field_ui/src/Tests/FieldUiTestTrait.php
index a597b97..ccb8751 100644
--- a/core/modules/field_ui/src/Tests/FieldUiTestTrait.php
+++ b/core/modules/field_ui/src/Tests/FieldUiTestTrait.php
@@ -81,7 +81,7 @@ public function fieldUIAddExistingField($bundle_path, $existing_storage_name, $l
     $label = $label ?: $this->randomString();
     $initial_edit = array(
       'existing_storage_name' => $existing_storage_name,
-      'label' => $label,
+      'existing_storage_label' => $label,
     );
 
     // First step: 'Re-use existing field' on the 'Add field' page.