diff --git a/ably.d.ts b/ably.d.ts
index 012de0fe3..e8bcbb3a3 100644
--- a/ably.d.ts
+++ b/ably.d.ts
@@ -650,7 +650,7 @@ export interface AuthOptions {
      * @param tokenRequestOrDetails - A valid `TokenRequest`, `TokenDetails` or Ably JWT to be used for authentication.
      */
     callback: (
-      error: ErrorInfo | string | null,
+      error: Error | string | null,
       tokenRequestOrDetails: TokenDetails | TokenRequest | string | null,
     ) => void,
   ): void;
diff --git a/src/common/lib/client/auth.ts b/src/common/lib/client/auth.ts
index d457ce10c..218ba4189 100644
--- a/src/common/lib/client/auth.ts
+++ b/src/common/lib/client/auth.ts
@@ -400,7 +400,7 @@ class Auth {
     let tokenRequestCallback: (
         data: API.TokenParams,
         callback: (
-          error: API.ErrorInfo | RequestResultError | string | null,
+          error: API.ErrorInfo | Error | RequestResultError | string | null,
           tokenRequestOrDetails: API.TokenDetails | API.TokenRequest | string | null,
           contentType?: string,
         ) => void,