diff --git a/colloscope/icalexport.py b/colloscope/icalexport.py
index b7ebc62..22d28a8 100644
--- a/colloscope/icalexport.py
+++ b/colloscope/icalexport.py
@@ -42,7 +42,7 @@ def to_calendar(etudiant, periode):
         event.add("categories", "COLLE-" + str(rotation.creneau.matiere))
 
         description = "Groupes: {','.join(str(groupe) for groupe in rotation.groupes.all())}"
-        event.add(description)
+        event.add("description", description)
 
         organizer = vCalAddress("mailto:unknown@mp2i-vms.fr")
         organizer.params["cn"] = vText(str(rotation.creneau.colleur))