OK, I figured it out (I think)

    [NonSerialized]

    EventHandler _nonSerializableHandlers;

    EventHandler _serializableHandlers;

    /// <summary>

    /// Declares a serialization-safe IsDirtyChanged event.

    /// </summary>

    public event EventHandler IsDirtyChanged

    {

      add

      {

        if (value.Target.GetType().IsSerializable)

          _serializableHandlers =

             (EventHandler)Delegate.Combine(_serializableHandlers, value);

        else

          _nonSerializableHandlers =

             (EventHandler)Delegate.Combine(_nonSerializableHandlers, value);

      }

      remove

      {

        if (value.Target.GetType().IsSerializable)

          _serializableHandlers =

            (EventHandler)Delegate.Remove(_serializableHandlers, value);

        else

          _nonSerializableHandlers =

            (EventHandler)Delegate.Remove(_nonSerializableHandlers, value);

      }

    }

    /// <summary>

    /// Call this method to raise the IsDirtyChanged event.

    /// </summary>

    virtual protected void OnIsDirtyChanged()

    {

      if (_nonSerializableHandlers != null)

        _nonSerializableHandlers(this, EventArgs.Empty);

      if (_serializableHandlers != null)

        _serializableHandlers(this, EventArgs.Empty);

    }

I temporarily forgot that C# makes you invoke the delegate directly anyway, so having a separate clause in the manual event declaration isn’t required. I still think it makes the code easier to read, but functionality is king in the end.