diff --git a/core/includes/form.inc b/core/includes/form.inc
index 58563c6..00c0ff6 100644
--- a/core/includes/form.inc
+++ b/core/includes/form.inc
@@ -193,9 +193,9 @@ function template_preprocess_fieldset(&$variables) {
   Element::setAttributes($element, array('id'));
   Element\RenderElement::setAttributes($element);
   $variables['attributes'] = $element['#attributes'];
-  $variables['prefix'] = isset($element['#field_prefix']) ? $element['#field_prefix'] : NULL;
-  $variables['suffix'] = isset($element['#field_suffix']) ? $element['#field_suffix'] : NULL;
-  $variables['title_display'] = isset($element['#title_display']) ? $element['#title_display'] : NULL;
+  $variables['prefix'] = $element['#field_prefix'];
+  $variables['suffix'] = $element['#field_suffix'];
+  $variables['title_display'] = $element['#title_display'];
   $variables['children'] = $element['#children'];
   $variables['required'] = !empty($element['#required']) ? $element['#required'] : NULL;
diff --git a/core/modules/system/src/Tests/Form/ElementsLabelsTest.php b/core/modules/system/src/Tests/Form/ElementsLabelsTest.php
index bf8d21c..360cb68 100644
--- a/core/modules/system/src/Tests/Form/ElementsLabelsTest.php
+++ b/core/modules/system/src/Tests/Form/ElementsLabelsTest.php
@@ -128,4 +128,27 @@ function testFormDescriptions() {
     $this->assertTrue(isset($elements[0]), t('Properly renders the #description element visually-hidden.'));
   }
 
+  /**
+   * Test forms in theme-less environments.
+   */
+  function testFormsInThemeLessEnvironments() {
+    $form = $this->getFormWithLimitedProperties();
+    $render_service = $this->container->get('renderer');
+    // This should not throw any notices.
+    $render_service->renderPlain($form);
+  }
+
+  /**
+   * Return a form with element with not all properties defined.
+   */
+  protected function getFormWithLimitedProperties() {
+    $form = array();
+
+    $form['fieldset'] = array(
+      '#type' => 'fieldset',
+      '#title' => 'Fieldset',
+    );
+
+    return $form;
+  }
 }