Generated gRPC C# code compilation error: Invalid token in class, record, struct, or interface member declaration

Question

I'm building a gRPC service with some proto files that are designed by a 3rd party. The service is built with .NET 5 and Grpc.AspNetCore 2.34.0.

When I'm adding the proto files to the project and try to build it, it fails with the error Invalid token '643_' in class, record, struct, or interface member declaration.

The C# code that is generated from the proto file seems to be the problem:

/// <summary>Field number for the "_64_3" field.</summary>
    public const int 643FieldNumber = 4;
    private static readonly pb::FieldCodec<ulong?> _single_643_codec = pb::FieldCodec.ForStructWrapper<ulong>(34);
    private ulong? 643_;
    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
    public ulong? 643 {
      get { return 643_; }
      set {
        643_ = value;
      }
    }

Class members are not supposed to begin with numbers. I can temporarily fix the compilation errors by putting an underscore before the member names. This is no solution ofc because the C# code is regenerated with every build of the project. This is what the relevant piece of the proto looks like:

message X_256B_IDType {
   google.protobuf.UInt64Value _64_0 = 1 [(validate.rules) = {message:{required:true}}];
   google.protobuf.UInt64Value _64_1 = 2 [(validate.rules) = {message:{required:true}}];
   google.protobuf.UInt64Value _64_2 = 3 [(validate.rules) = {message:{required:true}}];
   google.protobuf.UInt64Value _64_3 = 4 [(validate.rules) = {message:{required:true}}];
}

Is there a way to influence how the class members are generated using the Grpc.AspNetCore package? In any case, I have to adhere to the proto and not change the message contracts from an external viewpoint.