diff --git a/src/models/event.ts b/src/models/event.ts
index 5ae1187..bc32d88 100644
--- a/src/models/event.ts
+++ b/src/models/event.ts
@@ -114,8 +114,15 @@ export class EventObject implements EventInterface {
     }
 
     toJson(): EventInterface {
+        const data = {
+            ...this._data,
+            pattern: this._data.pattern instanceof EventOccurrenceObject
+                ? this._data.pattern.toJson()
+                : this._data.pattern,
+        };
+
         // Return a deep copy to avoid external modifications
-        return JSON.parse(JSON.stringify(this._data));
+        return JSON.parse(JSON.stringify(data));
     }
 
     clone(): EventObject {