diff --git a/divent/bot.py b/divent/bot.py
index 1b2e6ed..8b8767e 100644
--- a/divent/bot.py
+++ b/divent/bot.py
@@ -117,6 +117,9 @@ async def ical(guild_id: str):
 
     calendar = Calendar()
 
+    calendar.extra.append(ContentLine(name="REFRESH-INTERVAL", value="PT1H"))
+    calendar.extra.append(ContentLine(name="X-PUBLISHED-TTL", value="PT1H"))
+
     calendar.extra.append(ContentLine(name="NAME", value=guild.name))
     calendar.extra.append(ContentLine(name="X-WR-CALNAME", value=guild.name))