diff -u b/src/Form/FillPdfFormForm.php b/src/Form/FillPdfFormForm.php
--- b/src/Form/FillPdfFormForm.php
+++ b/src/Form/FillPdfFormForm.php
@@ -168,6 +168,20 @@
       $default_entity_id = count($stored_default_entity_id) ? $stored_default_entity_id->first()->value : NULL;
     }
 
+    $form['default_entity_id'] = [
+      '#title' => $this->t('Default entity'),
+      '#target_type' => $default_entity_type,
+      '#weight' => 13,
+      '#prefix' => '<div id="test-entity-wrapper">',
+      '#suffix' => '</div>',
+      '#ajax' => [
+        'callback' => '::ajaxUpdateEntityId',
+        'event' => 'autocompleteclose autocompletechange',
+        'wrapper' => 'test-entity-wrapper',
+        'progress' => ['type' => 'none'],
+      ],
+    ];
+
     // If a default entity type is set, allow selecting a default entity, too.
     if ($default_entity_type) {
       $storage = $this->entityTypeManager->getStorage($default_entity_type);
@@ -194,21 +208,10 @@
             '%type' => $default_entity_type,
           ]);
         }
-        $form['default_entity_id'] = [
+        $form['default_entity_id'] += [
           '#type' => 'entity_autocomplete',
-          '#title' => $this->t('Default entity'),
-          '#target_type' => $default_entity_type,
-          '#description' => $description,
-          '#weight' => 13,
           '#default_value' => $default_entity,
-          '#prefix' => '<div id="test-entity-wrapper">',
-          '#suffix' => '</div>',
-          '#ajax' => [
-            'callback' => '::ajaxUpdateEntityId',
-            'event' => 'autocompleteclose autocompletechange',
-            'wrapper' => 'test-entity-wrapper',
-            'progress' => ['type' => 'none'],
-          ],
+          '#description' => $description,
         ];
       }
       else {
@@ -221,34 +224,19 @@
             '%type' => $default_entity_type,
           ]);
         }
-        $form['default_entity_id'] = [
+        $form['default_entity_id'] += [
           '#type' => 'select',
-          '#title' => $this->t('Default entity'),
-          '#target_type' => $default_entity_type,
           '#options' => $options,
           '#empty_option' => $this->t('- None -'),
-          '#description' => $description,
-          '#weight' => 13,
           '#default_value' => $default_entity_id,
-          '#prefix' => '<div id="test-entity-wrapper">',
-          '#suffix' => '</div>',
-          '#ajax' => [
-            'callback' => '::ajaxUpdateEntityId',
-            'event' => 'change',
-            'wrapper' => 'test-entity-wrapper',
-            'progress' => ['type' => 'none'],
-          ],
+          '#description' => $description,
         ];
       }
     }
     // No default entity type set, so just provide a wrapper for AJAX replace.
     else {
-      $form['default_entity_id'] = [
+      $form['default_entity_id'] += [
         '#type' => 'hidden',
-        '#target_type' => NULL,
-        '#weight' => 13,
-        '#prefix' => '<div id="test-entity-wrapper">',
-        '#suffix' => '</div>',
       ];
     }