diff --git a/types/autobahn/index.d.ts b/types/autobahn/index.d.ts
index 3c576e2dc8..7f01a53e3a 100644
--- a/types/autobahn/index.d.ts
+++ b/types/autobahn/index.d.ts
@@ -205,7 +205,7 @@ declare namespace autobahn {
 
     type DeferFactory = () => When.Promise<any>;
 
-    type OnChallengeHandler = (session: Session, method: string, extra: any) => When.Promise<string>;
+    type OnChallengeHandler = (session: Session, method: string, extra: any) => string;
 
     interface IConnectionOptions {
         use_es6_promises?: boolean;