diff --git a/agenta-backend/agenta_backend/apis/fastapi/observability/utils.py b/agenta-backend/agenta_backend/apis/fastapi/observability/utils.py
index 71c6eac314..188f93cfa8 100644
--- a/agenta-backend/agenta_backend/apis/fastapi/observability/utils.py
+++ b/agenta-backend/agenta_backend/apis/fastapi/observability/utils.py
@@ -909,7 +909,7 @@ def parse_legacy_analytics(
     for bucket_dto in bucket_dtos:
         data_point = LegacyDataPoint(
             timestamp=bucket_dto.timestamp,
-            success_count=(bucket_dto.total.count - bucket_dto.error.count) or 0,
+            success_count=(bucket_dto.total.count or 0) - (bucket_dto.error.count or 0),
             failure_count=bucket_dto.error.count or 0,
             cost=bucket_dto.total.cost or 0.0,
             latency=bucket_dto.total.duration or 0.0,