diff --git a/core/modules/editor/src/Form/EditorImageDialog.php b/core/modules/editor/src/Form/EditorImageDialog.php
index 9c2feb5..1075852 100644
--- a/core/modules/editor/src/Form/EditorImageDialog.php
+++ b/core/modules/editor/src/Form/EditorImageDialog.php
@@ -63,14 +63,22 @@ public function getFormId() {
    *   The filter format for which this dialog corresponds.
    */
   public function buildForm(array $form, FormStateInterface $form_state, FilterFormat $filter_format = NULL) {
-    // The default values are set directly from \Drupal::request()->request,
-    // provided by the editor plugin opening the dialog.
-    if (!$image_element = $form_state->get('image_element')) {
-      $user_input = $form_state->getUserInput();
-      $image_element = isset($user_input['editor_object']) ? $user_input['editor_object'] : [];
-      $form_state->set('image_element', $image_element);
+    // This form is special, in that the default values do not come from the
+    // server side, but from the client side, from a text editor. We must cache
+    // this data in form state, because when the form is rebuilt, we will be
+    // receiving values from the form, instead of the values from the text
+    // editor. If we don't cache it, this data will be lost.
+    if (isset($form_state->getUserInput()['editor_object'])) {
+      // By convention, the data that the text editor sends to any dialog is in
+      // the 'editor_object' key. And the image dialog for text editors expects
+      // that data to be the attributes for an <img> element.
+      $form_state->set('image_element', $form_state->getUserInput()['editor_object']);
+      $form_state->setCached(TRUE);
     }
 
+    // Retrieve the image element's attributes from form state.
+    $image_element = $form_state->get('image_element');
+
     $form['#tree'] = TRUE;
     $form['#attached']['library'][] = 'editor/drupal.editor.dialog';
     $form['#prefix'] = '<div id="editor-image-dialog-form">';
diff --git a/core/modules/editor/src/Tests/EditorImageDialogTest.php b/core/modules/editor/src/Tests/EditorImageDialogTest.php
index 33e00ca..8350ea7 100644
--- a/core/modules/editor/src/Tests/EditorImageDialogTest.php
+++ b/core/modules/editor/src/Tests/EditorImageDialogTest.php
@@ -49,7 +49,7 @@ class EditorImageDialogTest extends EntityUnitTestBase {
   protected function setUp() {
     parent::setUp();
     $this->installEntitySchema('file');
-    $this->installSchema('system', ['router']);
+    $this->installSchema('system', ['router', 'key_value_expire']);
     $this->installSchema('node', array('node_access'));
     $this->installSchema('file', array('file_usage'));
     $this->installConfig(['node']);
@@ -123,10 +123,7 @@ public function testEditorImageDialog() {
     $request_stack->push($request);
     $form_builder = $this->container->get('form_builder');
     $form_object = new EditorImageDialog(\Drupal::entityManager()->getStorage('file'));
-    $form_id = $form_builder->getFormId($form_object, $form_state);
-    $form = $form_builder->retrieveForm($form_id, $form_state);
-    $form_builder->prepareForm($form_id, $form, $form_state);
-    $form_builder->processForm($form_id, $form, $form_state);
+    $form_builder->buildForm($form_object, $form_state);
 
     // Assert these two values are present and we don't get the 'not-this'
     // default back.