IMongoCollection中的OverflowException.UpdateOneAsync，尽管没有做算

我遇到了一个'System.OverflowException' in MongoDB.Bson.dll (Additional information: Arithmetic operation resulted in an overflow.)，调用UpdateOneAsync时不知道为什么:

CarSpec spec = GetSpec();
var updateDefinition = Builders<Cars>.Update.Set(c => c.Spec, spec);
IMongoCollection<CarBatch> carsBatch = GetCarsBatch();
var result = await carsBatch.UpdateOneAsync(c => c.Id == car.Id, updateDefinition);

这些是重要的数据结构:

public class Car {
    public string Id;
    public ServiceVersion CurrentVersion = new ServiceVersion();
    public CarSpec Spec = new CarSpec();
    public List<StatusNotice> StatusNotifications = new List<StatusNotice>();
}
public class CarSpec {
    internal const uint InitialChasisNumber = 1000000000;
    public uint ChasisNumber = InitialChasisNumber;
    public uint DoorsCount;
}

怎么了?