diff --git a/core/modules/editor/src/Form/EditorImageDialog.php b/core/modules/editor/src/Form/EditorImageDialog.php
index 8193cb67e1d88359ff5368a42bb0c8883f8cf972..ddcebb3a142607870de8d51f1dba1bf115a9853d 100644
--- a/core/modules/editor/src/Form/EditorImageDialog.php
+++ b/core/modules/editor/src/Form/EditorImageDialog.php
@@ -108,6 +108,7 @@ public function buildForm(array $form, FormStateInterface $form_state, FilterFor
     }
     $form['attributes']['alt'] = array(
       '#title' => $this->t('Alternative text'),
+      '#placeholder' => $this->t('Short description for the visually impaired'),
       '#type' => 'textfield',
       '#required' => TRUE,
       '#required_error' => $this->t('Alternative text is required.<br><em>(Only in rare cases should this be left empty. To create empty alternative text, enter <code>""</code> — two double quotes without any content).'),