diff --git a/install-dev/upgrade/php/fix_unique_specific_price.php b/install-dev/upgrade/php/fix_unique_specific_price.php
index f2f163731..0e794fa4e 100644
--- a/install-dev/upgrade/php/fix_unique_specific_price.php
+++ b/install-dev/upgrade/php/fix_unique_specific_price.php
@@ -28,17 +28,19 @@
 
 function fix_unique_specific_price()
 {
-	$res = Db::getInstance()->executeS('SELECT MIN(id_specific_price) id_specific_price
-													FROM '._DB_PREFIX_.'specific_price
-													GROUP BY `id_product`, `id_shop`, `id_currency`, `id_country`, `id_group`, `from_quantity`, `from`, `to`
-													');
-	if ($res)
-	{
-		$ids_specific_price = '(';
-		foreach ($res as $row)
-			$ids_specific_price .= (int)$row['id_specific_price'].',';
-		$ids_specific_price = rtrim($ids_specific_price, ',').')';
-		return Db::getInstance()->execute('DELETE FROM '._DB_PREFIX_.'specific_price 
-														WHERE id_specific_price NOT IN ('.$ids_specific_price.')');
-	}
-}
+	$result = Db::getInstance()->executeS('
+	SELECT MIN(id_specific_price) id_specific_price
+	FROM '._DB_PREFIX_.'specific_price
+	GROUP BY `id_product`, `id_shop`, `id_currency`, `id_country`, `id_group`, `from_quantity`, `from`, `to`');
+	if (!$result || !count($result))
+		return true; // return tru if there is not any specific price in the database
+		
+	$sql = '';
+	foreach ($result as $row)
+		$sql .= (int)$row['id_specific_price'].',';
+	$sql = rtrim($sql, ',');
+
+	return Db::getInstance()->execute('
+	DELETE FROM '._DB_PREFIX_.'specific_price 
+	WHERE id_specific_price NOT IN ('.$sql.')');
+}
\ No newline at end of file