diff --git a/lib/Persistent.ts b/lib/Persistent.ts
index f03bf51..89d2531 100644
--- a/lib/Persistent.ts
+++ b/lib/Persistent.ts
@@ -33,7 +33,7 @@ export abstract class Persistent implements Assignable, Serializable {
   }
 
   public to_object (): Record<string, PersistentType> {
-    return copy_object (this._data);
+    return copy_object (this._data) as Record<string, PersistentType>;
   }
 
   public serialize (formatted = false): string {