diff --git a/index.d.ts b/index.d.ts
index 777bda8..7fb609e 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -277,9 +277,10 @@ declare namespace OAuth2Server {
 
         /**
          * Invoked during request authentication to check if the provided access token was authorized the requested scopes.
+         * Optional, if a custom authenticateHandler is used or if there is no scope part of the request.
          *
          */
-        verifyScope(token: Token, scope: string | string[], callback?: Callback<boolean>): Promise<boolean>;
+        verifyScope?(token: Token, scope: string | string[], callback?: Callback<boolean>): Promise<boolean>;
     }
 
     interface AuthorizationCodeModel extends BaseModel, RequestAuthenticationModel {