diff --git a/lib/omise/res/OmiseApiResource.php b/lib/omise/res/OmiseApiResource.php
index 5f49170..455c4ca 100644
--- a/lib/omise/res/OmiseApiResource.php
+++ b/lib/omise/res/OmiseApiResource.php
@@ -1,8 +1,8 @@
 <?php
 
 define('OMISE_PHP_LIB_VERSION', '2.18.0');
-define('OMISE_API_URL', 'https://api.omise.co/');
-define('OMISE_VAULT_URL', 'https://vault.omise.co/');
+define('OMISE_API_URL', getenv('API_URL') ?: 'https://api.omise.co/');
+define('OMISE_VAULT_URL', getenv('VAULT_URL') ?: 'https://vault.omise.co/');
 
 #[\AllowDynamicProperties]
 class OmiseApiResource extends OmiseObject