diff -u b/core/includes/theme.inc b/core/includes/theme.inc
--- b/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -1630,15 +1630,9 @@
 
   // Creating variables for the template.
   $variables['entity_type'] = $element['#entity_type'];
-  $variables['field_name'] = strtr($element['#field_name'], '_', '-');
-  $variables['field_type'] = strtr($element['#field_type'], '_', '-');
-  $variables['field_label'] = strtr($element['#label_display'], '_', '-');
+  $variables['field_name'] = $element['#field_name'];
+  $variables['field_type'] = $element['#field_type'];
   $variables['label_display'] = $element['#label_display'];
-   // Are there multiple field items.
-  $variables['multiple'] = FALSE;
-  if (isset($element['#items']) && is_callable($element['#items']->getFieldDefinition(), 'isMultiple')) {
-    $variables['multiple'] = $element['#items']->getFieldDefinition()->isMultiple();
-  }
 
   $variables['label_hidden'] = ($element['#label_display'] == 'hidden');
   // Always set the field label - allow themes to decide whether to display it.
@@ -1651,9 +1645,15 @@
 
   // Creating variables for the template.
   $variables['entity_type'] = $element['#entity_type'];
-  $variables['field_name'] = $element['#field_name'];
-  $variables['field_type'] = $element['#field_type'];
+  $variables['field_name'] = strtr($element['#field_name'], '_', '-');
+  $variables['field_type'] = strtr($element['#field_type'], '_', '-');
+  $variables['field_label'] = strtr($element['#label_display'], '_', '-');
   $variables['label_display'] = $element['#label_display'];
+   // Are there multiple field items.
+  $variables['multiple'] = FALSE;
+  if (isset($element['#items']) && is_callable($element['#items']->getFieldDefinition(), 'isMultiple')) {
+    $variables['multiple'] = $element['#items']->getFieldDefinition()->isMultiple();
+  }
 
   $variables['label_hidden'] = ($element['#label_display'] == 'hidden');
   // Always set the field label - allow themes to decide whether to display it.
diff -u b/core/lib/Drupal/Core/Field/WidgetBase.php b/core/lib/Drupal/Core/Field/WidgetBase.php
--- b/core/lib/Drupal/Core/Field/WidgetBase.php
+++ b/core/lib/Drupal/Core/Field/WidgetBase.php
@@ -127,9 +127,9 @@
       '#parents' => array_merge($parents, array($field_name . '_wrapper')),
       '#attributes' => array(
         'class' => array(
-          'field--type-' . drupal_html_class($this->fieldDefinition->getType()),
-          'field--name-' . drupal_html_class($field_name),
-          'field--widget-' . drupal_html_class($this->getPluginId()),
+          'field--type-' . Html::getClass($this->fieldDefinition->getType()),
+          'field--name-' . Html::getClass($field_name),
+          'field--widget-' . Html::getClass($this->getPluginId()),
         ),
       ),
       'widget' => $elements,