diff --git a/src/externalldap.js b/src/externalldap.js
index 177150fa3..02e8cce4e 100644
--- a/src/externalldap.js
+++ b/src/externalldap.js
@@ -46,7 +46,7 @@ function translateUser(ldapConfig, ldapUser) {
 
     // RFC: https://datatracker.ietf.org/doc/html/rfc2798
     const user = {
-        username: typeof ldapUser[ldapConfig.usernameField] !== 'string' ? ldapUser[ldapConfig.usernameField].toLowerCase() : '',
+        username: typeof ldapUser[ldapConfig.usernameField] === 'string' ? ldapUser[ldapConfig.usernameField].toLowerCase() : '',
         email: ldapUser.mail || ldapUser.mailPrimaryAddress,
         twoFactorAuthenticationEnabled: !!ldapUser.twoFactorAuthenticationEnabled,
         displayName: ldapUser.displayName || ldapUser.cn // user.giveName + ' ' + user.sn