diff --git a/app/code/Mage/Catalog/Model/Product/Type/Price.php b/app/code/Mage/Catalog/Model/Product/Type/Price.php
index 9139ddb1026c3..d71cabc832661 100644
--- a/app/code/Mage/Catalog/Model/Product/Type/Price.php
+++ b/app/code/Mage/Catalog/Model/Product/Type/Price.php
@@ -254,7 +254,7 @@ public function getTierPrice($qty = null, $product)
 
     protected function _getCustomerGroupId($product)
     {
-        if ($product->getCustomerGroupId()) {
+        if (!is_null($product->getCustomerGroupId())) {
             return $product->getCustomerGroupId();
         }
         return Mage::getSingleton('Mage_Customer_Model_Session')->getCustomerGroupId();