How can I define this struct in my COM library?

I created a new ATL project in Visual Studio 2015. I added a new simple ATL object, inside of the library I am trying to define a struct so that I may pass this struct around in my COM implementation. Here is my CerberusNative.idl definition, with the added CerberusErrorDetails structure:

import "oaidl.idl";
import "ocidl.idl";

[
    object,
    uuid(B98A7D3F-651A-49BE-9744-2B1D8C896E9E),
    dual,
    nonextensible,
    pointer_default(unique)
]
interface ICerberusSession : IDispatch{
};
[
    uuid(8F2227F9-10A9-4114-A683-3CBEB02BD6DA),
    version(1.0),
]
library CerberusNativeLib
{
    [
        uuid(527568A1-36A8-467A-82F5-228F7C3AC926)
    ]
    typedef struct CerberusErrorDetails
    {
        INT ErrorCode;
        BSTR ErrorMessage;
    };
    importlib("stdole2.tlb");
    [
        uuid(CAB8A88E-CE0E-4B4C-B656-C52A7C8A5B18)      
    ]
    coclass CerberusSession
    {
        [default] interface ICerberusSession;
    };
};

When I try to compile it, I get the following error:

Error MIDL2312 illegal syntax unless using mktyplib compatibility mode : CerberusErrorDetails CerberusNative CerberusNative.idl 32

Am I doing something wrong? What is this mktyplib error? Why is it asking for it?

Syntax was wrong. Correct way:

    typedef
        [
            uuid(527568A1-36A8-467A-82F5-228F7C3AC926),
            version(1.0)
        ]
    struct CerberusErrorDetails {
        INT ErrorCode;
        BSTR ErrorMessage;
    } CerberusErrorDetails;