diff --git a/calendar/lightning/content/calendar-management.js b/calendar/lightning/content/calendar-management.js
index a28a3f6a3a1..28f22f3ace7 100644
--- a/calendar/lightning/content/calendar-management.js
+++ b/calendar/lightning/content/calendar-management.js
@@ -148,6 +148,7 @@ function getCompositeCalendar()
         activeCompositeCalendar =
             ltnCreateInstance("@mozilla.org/calendar/calendar;1?type=composite",
                               "calICompositeCalendar");
+        activeCompositeCalendar.prefPrefix = "lightning-main";
         activeCompositeCalendar.addObserver(ltnCompositeCalendarObserver, 0);
     }