diff --git a/core/themes/claro/claro.theme b/core/themes/claro/claro.theme
index a3eee603df..0380bdfbd6 100644
--- a/core/themes/claro/claro.theme
+++ b/core/themes/claro/claro.theme
@@ -825,10 +825,12 @@ function claro_preprocess_field_multiple_value_form(&$variables) {
 
   if ($variables['multiple']) {
     // Add an additional CSS class to the field label table cell. The table
-    // header cell exists always in a multiple value field.
+    // header cell should always exist unless removed by contrib.
     // @see template_preprocess_field_multiple_value_form().
-    $variables['table']['#header'][0]['data']['#attributes']['class'][] = 'form-item__label';
-    $variables['table']['#header'][0]['data']['#attributes']['class'][] = 'form-item__label--multiple-value-form';
+    if (isset($variables['table']['#header'][0]['data']['#attributes']) && $variables['table']['#header'][0]['data']['#attributes'] instanceof Attribute) {
+      $variables['table']['#header'][0]['data']['#attributes']->removeClass('label');
+      $variables['table']['#header'][0]['data']['#attributes']->addClass('form-item__label', 'form-item__label--multiple-value-form');
+    }
 
     if ($variables['disabled']) {
       $variables['table']['#attributes']['class'][] = 'tabledrag-disabled';