diff --git a/calendar/base/public/calICalendarViewController.idl b/calendar/base/public/calICalendarViewController.idl
index 63f295579dcc..d0407b8c5f44 100644
--- a/calendar/base/public/calICalendarViewController.idl
+++ b/calendar/base/public/calICalendarViewController.idl
@@ -42,7 +42,7 @@
 interface calICalendar;
 interface calIDateTime;
 interface calIEvent;
-interface calIItemOccurrence;
+interface calIItemBase;
 
 [scriptable, uuid(1f783898-f4c2-4b2d-972e-360e0de38237)]
 interface calICalendarViewController : nsISupports
@@ -76,7 +76,7 @@ interface calICalendarViewController : nsISupports
    * Modify aOccurrence.  If aNewStartTime and aNewEndTime are given,
    * update the event to those times.  Otherwise ask the user to modify.
    */
-  void modifyOccurrence (in calIItemOccurrence aOccurrence,
+  void modifyOccurrence (in calIItemBase aOccurrence,
 			 in calIDateTime aNewStartTime,
 			 in calIDateTime aNewEndTime);
 
@@ -85,6 +85,6 @@ interface calICalendarViewController : nsISupports
    * just this occurrence or all occurrences, and do whatever else
    * is appropriate.
    */
-  void deleteOccurrence (in calIItemOccurrence aOccurrence);
+  void deleteOccurrence (in calIItemBase aOccurrence);
 };
 
diff --git a/calendar/base/public/calIRecurrenceInfo.idl b/calendar/base/public/calIRecurrenceInfo.idl
index 185caa2b39b4..99c14e270cd2 100644
--- a/calendar/base/public/calIRecurrenceInfo.idl
+++ b/calendar/base/public/calIRecurrenceInfo.idl
@@ -159,7 +159,7 @@ interface calIRecurrenceInfo : nsISupports
                            out unsigned long aCount, [array,size_is(aCount),retval] out calIDateTime aDates);
 
   /**
-   * Return an array of calIItemOccurrence representing all
+   * Return an array of calIItemBase representing all
    * occurrences of this event between start (inclusive) and end (non-inclusive).
    */
   void getOccurrences (in calIDateTime aRangeStart,
diff --git a/calendar/base/public/calIRecurrenceItem.idl b/calendar/base/public/calIRecurrenceItem.idl
index 83ea857aeef1..1f9f41e2833f 100644
--- a/calendar/base/public/calIRecurrenceItem.idl
+++ b/calendar/base/public/calIRecurrenceItem.idl
@@ -40,7 +40,6 @@
 
 interface calIItemBase;
 interface calIDateTime;
-interface calIItemOccurrence;
 
 interface calIIcalProperty;
 
diff --git a/calendar/providers/memory/calMemoryCalendar.js b/calendar/providers/memory/calMemoryCalendar.js
index bb617365ff3a..f8f9a05d97b3 100644
--- a/calendar/providers/memory/calMemoryCalendar.js
+++ b/calendar/providers/memory/calMemoryCalendar.js
@@ -348,7 +348,6 @@ calMemoryCalendar.prototype = {
         const calIItemBase = Components.interfaces.calIItemBase;
         const calIEvent = Components.interfaces.calIEvent;
         const calITodo = Components.interfaces.calITodo;
-        const calIItemOccurrence = Components.interfaces.calIItemOccurrence;
         const calIRecurrenceInfo = Components.interfaces.calIRecurrenceInfo;
 
         var itemsFound = Array();