diff --git a/sync.py b/sync.py
index 8ac387c..abb8a2e 100644
--- a/sync.py
+++ b/sync.py
@@ -19,18 +19,16 @@ for login, content in auth['logins'].items():
     logins[login] = caldav.DAVClient(url=content['url'], username=content['user'], password=content['password'])
 
 cals = []
+cal_evts = {}
 for cal in auth['cals']:
     cals.append(caldav.Calendar(client = logins[cal['login']], url = cal['url']))
+    cal_evts[cals[-1].canonical_url] = [ evt.vobject_instance.vevent.uid.value for evt in cals[-1].events() ]
 
 changed = {}
 deleted = {}
 
 def cal_contains_uid(cal, uid):
-    try:
-        event = cal.event_by_uid(uid)
-        return True
-    except caldav.lib.error.NotFoundError:
-        return False
+    return uid in cal_evts[cal.canonical_url]
 
 for cal in cals:
     print("Checking %s" % (cal.canonical_url,))