diff --git a/src/Exceptions.php b/src/Exceptions.php
index f208b6e..2a40a1a 100644
--- a/src/Exceptions.php
+++ b/src/Exceptions.php
@@ -26,6 +26,8 @@ class TokenExpiredException extends AuthException {}
 
 class TooManyRequestsException extends AuthException {}
 
+class DuplicateUsernameException extends AuthException {}
+
 class AuthError extends \Exception {}
 
 class DatabaseError extends AuthError {}