diff --git a/src/View/Helper/FormHelper.php b/src/View/Helper/FormHelper.php
index 20f5d10c..4e4ccd58 100644
--- a/src/View/Helper/FormHelper.php
+++ b/src/View/Helper/FormHelper.php
@@ -647,7 +647,9 @@ protected function _containerOptions(?string $fieldName, array $options): array
             isset($options['type']) &&
             $options['spacing'] !== false
         ) {
-            $options['container'] = $this->injectClasses($options['spacing'], (array)($options['container'] ?? []));
+            $classes = $options['spacing'] ?? [];
+            $options = (array)($options['container'] ?? []);
+            $options['container'] = $this->injectClasses($classes, $options);
         }
 
         if (