diff --git a/data/class/SC_Product.php b/data/class/SC_Product.php
index c89b8e4565..9b99d0beb9 100644
--- a/data/class/SC_Product.php
+++ b/data/class/SC_Product.php
@@ -298,7 +298,7 @@ public function setProductsClassByProductIds($arrProductId, $has_deleted = false
                     $this->stock_find[$productId] = true;
                 }
 
-                if (!in_array($classcategory_id1, $classCats1)) {
+                if (!in_array($classcategory_id1, array_keys($classCats1))) {
                     $classCats1[$classcategory_id1] = $arrProductsClass['classcategory_name1']
                         . ($classcategory_id2 == 0 && !$stock_find_class ? ' (品切れ中)' : '');
                 }