diff --git a/mpicms/events/models.py b/mpicms/events/models.py
index a0494aa..bc7fa3e 100644
--- a/mpicms/events/models.py
+++ b/mpicms/events/models.py
@@ -122,9 +122,14 @@ def clean(self):  # Prevent more than one event index
 
     def get_ics(self, external=False):
         c = Calendar()
-        for event in self.events.filter(external=external):
+        # ics 0.7 keeps events in a set, which serializes in random order.
+        # The serializer only iterates over it, so a list keeps our order.
+        c.events = []
+        events = self.events.filter(external=external).order_by('-start_date', '-start_time', '-pk')
+        for event in events:
             e = ICSEvent(
                 name=event.title,
+                uid='event-%d@intranet.molgen.mpg.de' % event.pk,
                 begin=event.start,
                 end=event.end,
                 description=event.search_description,
@@ -133,7 +138,7 @@ def get_ics(self, external=False):
             )
             if type(event.start) is date:
                 e.make_all_day()
-            c.events.add(e)
+            c.events.append(e)
         return c