diff --git a/src/qtism/runtime/rendering/markup/xhtml/ChoiceInteractionRenderer.php b/src/qtism/runtime/rendering/markup/xhtml/ChoiceInteractionRenderer.php
index <HASH>..<HASH> 100644
--- a/src/qtism/runtime/rendering/markup/xhtml/ChoiceInteractionRenderer.php
+++ b/src/qtism/runtime/rendering/markup/xhtml/ChoiceInteractionRenderer.php
@@ -65,6 +65,7 @@ class ChoiceInteractionRenderer extends InteractionRenderer
         parent::appendAttributes($fragment, $component, $base);
         $this->additionalClass('qti-blockInteraction');
         $this->additionalClass('qti-choiceInteraction');
+        $this->additionalUserClass(($component->getOrientation() === Orientation::VERTICAL) ? 'qti-vertical' : 'qti-horizontal');
 
         $fragment->firstChild->setAttribute('data-shuffle', ($component->mustShuffle() === true) ? 'true' : 'false');
         $fragment->firstChild->setAttribute('data-max-choices', $component->getMaxChoices());
missing additional user CSS class 'qti-vertical'/'qti-horinzontal'.