diff --git a/dist/oidc-client.d.ts b/dist/oidc-client.d.ts
index 9ca7b6f3..cc05b391 100644
--- a/dist/oidc-client.d.ts
+++ b/dist/oidc-client.d.ts
@@ -208,7 +208,7 @@ export class UserManager extends OidcClient {
   signinCallback(url?: string): Promise<User>;
 
   /** Proxy to Popup and Redirect callbacks */
-  signoutCallback(url?: string, keepWindowOpen?: boolean): Promise<SignoutResponse | void>;
+  signoutCallback(url?: string, keepWindowOpen?: boolean): Promise<SignoutResponse | undefined>;
 
   /** Query OP for user's current signin status */
   querySessionStatus(args?: any): Promise<SessionStatus>;
diff --git a/index.d.ts b/index.d.ts
index 03f4f80c..ef62ccd1 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -213,7 +213,7 @@ export class UserManager extends OidcClient {
   signinCallback(url?: string): Promise<User>;
 
   /** Proxy to Popup and Redirect callbacks */
-  signoutCallback(url?: string, keepWindowOpen?: boolean): Promise<SignoutResponse | void>;
+  signoutCallback(url?: string, keepWindowOpen?: boolean): Promise<SignoutResponse | undefined>;
 
   /** Query OP for user's current signin status */
   querySessionStatus(args?: any): Promise<SessionStatus>;