NotSupportedException thrown by SqlConnection.Execute when updating with Dapper

I'm attempting to use Dapper to update the records found in one of my Database tables. The table itself is described as below.

ID          int
AppId       nvarchar(MAX)
Created     datetime2(7)
Updated     datetime2(7)
Data        nvarchar(MAX)

The object going into the table is defined in C# code as follows:

public class Schema
    {
        public int ID { get; set; }
        public string AppId { get; set; }
        public DateTime Created { get; set; }
        public DateTime Updated { get; set; }
        public string Data { get; set; }
    }

But when I execute the code below I get a NotSupportedException: The member newSchema of type Schema cannot be used as a parameter value

public int UpdateSchema(Schema newSchema, int idToUpdate)
        {
            var sql = "UPDATE Schemas " +
                         "SET schema = @newSchema " +
                         "WHERE ID = @idToUpdate";

            var result = _connection.Execute(sql, new {newSchema, idToUpdate});
            return result;
        }

Why exactly is this happening and what can I do to prevent it? I know that my Schema class is compitable with my database table as when I attempt to create new Schema records in the table it executes my query without any issues.