diff --git a/src/transport_performance/gtfs/multi_validation.py b/src/transport_performance/gtfs/multi_validation.py
index 2539616b..8d6d5037 100644
--- a/src/transport_performance/gtfs/multi_validation.py
+++ b/src/transport_performance/gtfs/multi_validation.py
@@ -19,6 +19,7 @@
     _check_parent_dir_exists,
     _enforce_file_extension,
 )
+from transport_performance.gtfs.calendar import create_calendar_from_dates
 
 
 class MultiGtfsInstance:
@@ -111,6 +112,25 @@ def __init__(self, path: Union[str, list, pathlib.Path]) -> None:
         self.paths = path
         # instantiate the GtfsInstance's
         self.instances = [GtfsInstance(fpath) for fpath in path]
+        # ensure calendar is populated
+        for i, inst in enumerate(self.instances):
+            if inst.feed.calendar is None:
+                if inst.feed.calendar_dates is None:
+                    raise FileNotFoundError(
+                        "Both calendar and calendar_dates is empty for feed "
+                        + self.paths[i]
+                    )
+                else:
+                    warnings.warn(
+                        f"No calendar found for {self.paths[i]}. Creating from"
+                        " calendar dates"
+                    )
+                    # store calendar_dates
+                    self.instances[
+                        i
+                    ].feed.calendar = create_calendar_from_dates(
+                        calendar_dates=inst.feed.calendar_dates
+                    )
 
     def save_feeds(self, dir: Union[pathlib.Path, str]) -> None:
         """Save the GtfsInstances to a directory.