diff --git a/validate_yaml.py b/validate_yaml.py
index a24a5d5..0ee272d 100755
--- a/validate_yaml.py
+++ b/validate_yaml.py
@@ -25,6 +25,7 @@ data_dir = config.PERSONAL_DATA
 currencies = set(config.CURRENCIES + ["GBP"])
 
 LatLon = Tuple[float, float]
+MAX_TRIP_NIGHTS = 60
 
 
 def check_currency(item: agenda.types.StrDict) -> None:
@@ -102,6 +103,22 @@ def ranges_overlap(
     return start_a < end_b and start_b < end_a
 
 
+def check_trip_duration(trip: agenda.types.Trip) -> None:
+    """Check trip duration is within the expected maximum."""
+    if trip.end is None:
+        return
+
+    nights = (trip.end - trip.start).days
+    if nights <= MAX_TRIP_NIGHTS:
+        return
+
+    url = f"https://edwardbetts.com/agenda/trip/{trip.start.isoformat()}"
+    print(f"Trip is too long: {url}")
+    print(f"  {trip.title}")
+    print(f"  {trip.start.isoformat()} to {trip.end.isoformat()}: {nights} nights")
+    assert False, f"Trip is {nights} nights; maximum is {MAX_TRIP_NIGHTS}"
+
+
 def check_trips() -> None:
     """Check trips and ensure they are in chronological order."""
     filepath = os.path.join(data_dir, "trips.yaml")
@@ -130,6 +147,8 @@ def check_trips() -> None:
     print(len(trip_list), "trips")
 
     for trip in trip_list:
+        check_trip_duration(trip)
+
         if not trip.accommodation or not trip.conferences:
             continue
         accommodation_entries: list[