diff --git a/htdocs/api/class/api_setup.class.php b/htdocs/api/class/api_setup.class.php
index 1b619acfeb7..5dbccb69fb4 100644
--- a/htdocs/api/class/api_setup.class.php
+++ b/htdocs/api/class/api_setup.class.php
@@ -1426,7 +1426,7 @@ class Setup extends DolibarrApi
     		throw new RestException(403, 'Error API open to admin users only or to the login user defined with constant API_LOGIN_ALLOWED_FOR_ADMIN_CHECK');
     	}
 
-    	if (! preg_match('/[^a-zA-Z0-9_]/', $confname) || ! isset($conf->global->$confname)) {
+    	if (! preg_match('/[a-zA-Z0-9_]/', $confname) || ! isset($conf->global->$confname)) {
     		throw new RestException(500, 'Error Bad or unknown value for constname');
     	}
     	if (preg_match('/(_pass|password|secret|_key|key$)/i', $confname)) {