diff --git a/types/oauth2-server/index.d.ts b/types/oauth2-server/index.d.ts
index 6729a05e7e..6c20aab221 100644
--- a/types/oauth2-server/index.d.ts
+++ b/types/oauth2-server/index.d.ts
@@ -1,7 +1,8 @@
 // Type definitions for Node OAuth2 Server 3.0
 // Project: https://github.com/oauthjs/node-oauth2-server
 // Definitions by:  Robbie Van Gorkom <https://github.com/vangorra>,
-//                  Charles Irick <https://github.com/cirick>
+//                  Charles Irick <https://github.com/cirick>,
+//                  Daniel Fischer <https://github.com/d-fischer>
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 // TypeScript Version: 2.2
 
@@ -263,7 +264,7 @@ declare namespace OAuth2Server {
          * Invoked to check if the requested scope is valid for a particular client/user combination.
          *
          */
-        validateScope?(user: User, client: Client, scope: string, callback?: Callback<string[] | Falsey>): Promise<string[] | Falsey>;
+        validateScope?(user: User, client: Client, scope: string, callback?: Callback<string | Falsey>): Promise<string | Falsey>;
     }
 
     interface PasswordModel extends BaseModel, RequestAuthenticationModel {
@@ -283,7 +284,7 @@ declare namespace OAuth2Server {
          * Invoked to check if the requested scope is valid for a particular client/user combination.
          *
          */
-        validateScope?(user: User, client: Client, scope: string, callback?: Callback<string[] | Falsey>): Promise<string[] | Falsey>;
+        validateScope?(user: User, client: Client, scope: string, callback?: Callback<string | Falsey>): Promise<string | Falsey>;
     }
 
     interface RefreshTokenModel extends BaseModel, RequestAuthenticationModel {
@@ -317,7 +318,7 @@ declare namespace OAuth2Server {
          * Invoked to check if the requested scope is valid for a particular client/user combination.
          *
          */
-        validateScope?(user: User, client: Client, scope: string, callback?: Callback<string[] | Falsey>): Promise<string[] | Falsey>;
+        validateScope?(user: User, client: Client, scope: string, callback?: Callback<string | Falsey>): Promise<string | Falsey>;
     }
 
     interface ExtensionModel extends BaseModel, RequestAuthenticationModel {}
@@ -380,6 +381,39 @@ declare namespace OAuth2Server {
         user: User;
         [key: string]: any;
     }
+
+    class OAuthError extends Error {
+        constructor(messageOrError: string | Error, properties?: object);
+
+        /**
+         * The HTTP error code.
+         */
+        code: number;
+
+        /**
+         * The OAuth error code.
+         */
+        name: string;
+
+        /**
+         * A human-readable error message.
+         */
+        message: string;
+    }
+
+    class AccessDeniedError extends OAuthError {}
+    class InsufficientScopeError extends OAuthError {}
+    class InvalidArgumentError extends OAuthError {}
+    class InvalidClientError extends OAuthError {}
+    class InvalidGrantError extends OAuthError {}
+    class InvalidRequestError extends OAuthError {}
+    class InvalidScopeError extends OAuthError {}
+    class InvalidTokenError extends OAuthError {}
+    class ServerError extends OAuthError {}
+    class UnauthorizedClientError extends OAuthError {}
+    class UnauthorizedRequestError extends OAuthError {}
+    class UnsupportedGrantTypeError extends OAuthError {}
+    class UnsupportedResponseTypeError extends OAuthError {}
 }
 
 export = OAuth2Server;