diff --git a/src/OAuth2/Storage/Pdo.php b/src/OAuth2/Storage/Pdo.php
index b8fac34ab..e7f35f648 100644
--- a/src/OAuth2/Storage/Pdo.php
+++ b/src/OAuth2/Storage/Pdo.php
@@ -463,7 +463,7 @@ public function getBuildSql($dbName = 'oauth2_server_php')
         $sql = "
         CREATE TABLE {$this->config['client_table']} (
           client_id             VARCHAR(80)   NOT NULL,
-          client_secret         VARCHAR(80)   NOT NULL,
+          client_secret         VARCHAR(80),
           redirect_uri          VARCHAR(2000),
           grant_types           VARCHAR(80),
           scope                 VARCHAR(4000),