Can't convert List to ICollection - Fluent API

问题:

I've done this before, I don't know why this is throwing me errors.

These are my classes:

public class ChatModel
{
    public int ChatID { get; set; }
    public virtual List<ChatModel> Messages { get; set; }
}

public class MessageModel
{
    public int MessageID { get; set; }
    public string Issuer { get; set; }
    public string Message { get; set; }
    public ChatModel Chat { get; set; }
}

And this is what I'm doing through Fluent API:

modelBuilder.Entity<ChatModel>()
            .HasMany<MessageModel>(c => c.Messages)
            .WithRequired(m => m.Chat);

The line that's giving me errors is this one:

.HasMany<MessageModel>(c => c.Messages)

It says:

Error CS0266 Cannot implicitly convert type 'System.Collections.Generic.List' to 'System.Collections.Generic.ICollection'. An explicit conversion exists (are you missing a cast?)

But honestly, I have absolutely no idea, I've done exactly the same thing with other classes while creating other relationships. But this one is giving me a headache.

Can anybody tell me what I'm doing wrong? Thanks in advance. :)