diff --git a/meta.go b/meta.go
index 573a8d0..eb344a3 100644
--- a/meta.go
+++ b/meta.go
@@ -1,12 +1,14 @@
 package meta
 
+const classField = "$id"
+
 func ReadGeneric(r Reader, createFunc StructFactory, field string) (Readable, error) {
 	if err := r.BeginContainer(field); err != nil {
 		return nil, err
 	}
 
 	var classId uint32
-	if err := r.ReadUint32(&classId, ""); err != nil {
+	if err := r.ReadUint32(&classId, classField); err != nil {
 		return nil, err
 	}
 
@@ -30,7 +32,7 @@ func WriteGeneric(w Writer, s WritableClass, field string) error {
 	if err := w.BeginCollection(s.FieldsCount()+1, field); err != nil {
 		return err
 	}
-	if err := w.WriteUint32(s.ClassId(), ""); err != nil {
+	if err := w.WriteUint32(s.ClassId(), classField); err != nil {
 		return err
 	}
 	if err := s.WriteFields(w); err != nil {