diff --git a/lib/Persistent.ts b/lib/Persistent.ts
index 1afad0f..668f767 100644
--- a/lib/Persistent.ts
+++ b/lib/Persistent.ts
@@ -31,8 +31,8 @@ export abstract class Persistent implements Assignable, Serializable {
 
   public serialize (formatted = false): string {
     if (formatted)
-      return JSON.stringify (this.to_object ());
-    return JSON.stringify (this.to_object (), null, 2);
+      return JSON.stringify (this._data);
+    return JSON.stringify (this._data, null, 2);
   }
 
   private check_type (value: unknown, prop: PersistentTypeString): boolean {