diff --git a/src/core/schedules/schedulejson.py b/src/core/schedules/schedulejson.py
index a4ecf60205e6dc9266a3580e1aaa4f5d1d0afa2b..f6c92eaab1bd7d66db490e0ba30d121b2c68ce73 100644
--- a/src/core/schedules/schedulejson.py
+++ b/src/core/schedules/schedulejson.py
@@ -104,7 +104,7 @@ class ScheduleJSONSupport(BaseScheduleSupport):
         if self.conf_value('feedback'):
             data['feedback_url'] = f"{event['url']}feedback/"
         if self.conf_value('legacy_id_offset'):
-            data['id'] = event['id'] + self.conf_value('legacy_id_offset')
+            data['id'] = int(event['id']) + int(self.conf_value('legacy_id_offset') or 0)
 
         return data