Stephen Mustgrave
--- a/core/modules/text/src/Plugin/Field/FieldType/TextWithSummaryItem.php
+++ b/core/modules/text/src/Plugin/Field/FieldType/TextWithSummaryItem.php
      '#type' => 'checkbox',
      '#title' => $this->t('Require summary'),
-      '#description' => $this->t('The summary will also be visible when marked as required.'),
+      '#description' => $this->t('Enable "Summary input" and "Require summary" to make the summary required.'),
+      '#element_validate' => [[static::class, 'validateRequiredSummary']],
      '#default_value' => $settings['required_summary'],
+      '#states' => [
+        'visible' => [
+          ':input[name="settings[display_summary]"]' => ['checked' => TRUE],
+        ],
+        'enabled' => [
+          ':input[name="settings[display_summary]"]' => ['checked' => TRUE],
+        ],
+        'unchecked' => [
+          ':input[name="settings[required_summary]"]' => ['checked' => FALSE],
+        ],
--- a/core/modules/text/src/Plugin/Field/FieldType/TextWithSummaryItem.php
+++ b/core/modules/text/src/Plugin/Field/FieldType/TextWithSummaryItem.php
+   * This function is assigned as an #element_validate callback in
+   * fieldSettingsForm().
+   */
+  public static function validateRequiredSummary($element, FormStateInterface $form_state) {
+    if (!empty($element['#value']) && empty($form_state->getValue(['settings', 'display_summary']))) {
+      $form_state->setError($element, t('If "Require summary" is checked "Summary input" has to be checked as well.'));
+    }
+  }
+
  /**
   * {@inheritdoc}
   */
  public function getConstraints() {
    $constraints = parent::getConstraints();
-    if ($this->getSetting('required_summary')) {
+    if ($this->getSetting('required_summary') && $this->getSetting('display_summary')) {
--- a/core/modules/text/src/Plugin/Field/FieldWidget/TextareaWithSummaryWidget.php
+++ b/core/modules/text/src/Plugin/Field/FieldWidget/TextareaWithSummaryWidget.php
    $element = parent::formElement($items, $delta, $element, $form, $form_state);

    $display_summary = $items[$delta]->summary || $this->getFieldSetting('display_summary');
-    $required = empty($form['#type']) && $this->getFieldSetting('required_summary');
+    $required = $display_summary && !$form_state->has('default_value_widget') && $this->getFieldSetting('required_summary');