How do I bootstrap Automapper with Nancy in .Net Core?

How do I bootstrap Automapper with Nancy in .Net Core? I am using the Automapper.Extensions.Microsoft.DependencyInjection nuget package, whereby I call services.AddAutoMapper(); in Startup.ConfigureServices. The profile within my Nancy assembly is registered, but profiles in external assemblies are not. I don't have this problem with Asp.Net Core.

I'm using Nancy v2.0.0-clinteastwood, Automapper 7.0.1, Automapper.Extensions.Microsoft.DependencyInjection 5.0.1 and .Net Core v2.1.

My DI container is Autofac v4.3