diff --git a/agenda/conference.py b/agenda/conference.py
index 9960f80..36f6e06 100644
--- a/agenda/conference.py
+++ b/agenda/conference.py
@@ -6,8 +6,11 @@ from datetime import date, datetime
 
 import yaml
 
+from . import utils
 from .event import Event
 
+MAX_CONF_DAYS = 20
+
 
 @dataclasses.dataclass
 class Conference:
@@ -55,6 +58,9 @@ def get_list(filepath: str) -> list[Event]:
     """Read conferences from a YAML file and return a list of Event objects."""
     events: list[Event] = []
     for conf in (Conference(**conf) for conf in yaml.safe_load(open(filepath, "r"))):
+        assert conf.start <= conf.end
+        duration = (utils.as_date(conf.end) - utils.as_date(conf.start)).days
+        assert duration < MAX_CONF_DAYS
         event = Event(
             name="conference",
             date=conf.start,