diff --git a/includes/theme.inc b/includes/theme.inc
index 5325ff7..453cb49 100644
--- a/includes/theme.inc
+++ b/includes/theme.inc
@@ -1828,6 +1828,9 @@ function theme_item_list($variables) {
           elseif ($key == 'children') {
             $children = $value;
           }
+          elseif ($key == 'class' && is_string($value)) {
+            $attributes['class'][] = $value;
+          }
           else {
             $attributes[$key] = $value;
           }