diff --git a/src/transport_performance/gtfs/multi_validation.py b/src/transport_performance/gtfs/multi_validation.py
index 8d6d5037..bf164bd7 100644
--- a/src/transport_performance/gtfs/multi_validation.py
+++ b/src/transport_performance/gtfs/multi_validation.py
@@ -117,7 +117,7 @@ def __init__(self, path: Union[str, list, pathlib.Path]) -> None:
             if inst.feed.calendar is None:
                 if inst.feed.calendar_dates is None:
                     raise FileNotFoundError(
-                        "Both calendar and calendar_dates is empty for feed "
+                        "Both calendar and calendar_dates are empty for feed "
                         + self.paths[i]
                     )
                 else: