--- a/calendar/base/src/calFilter.js
+++ b/calendar/base/src/calFilter.js
@@ -793,30 +793,28 @@ calFilter.prototype = {
         if (!next) {
           // there are no more occurrences
           return null;
         }
 
         if (this.isItemInFilters(next)) {
           return next;
         }
-        next.QueryInterface(Ci.calIEvent);
         start = next.startDate || next.entryDate;
       }
 
       // we've hit the maximum number of iterations without finding a match
       cal.WARN("[calFilter] getNextOccurrence: reached maximum iterations for " + aItem.title);
       return null;
     } else {
       // the parent item doesn't match the filter, we can return the first future exception
       // that matches the filter
       let exMatch = null;
       aItem.recurrenceInfo.getExceptionIds({}).forEach(function(rID) {
         let ex = aItem.recurrenceInfo.getExceptionFor(rID);
-        ex.QueryInterface(Ci.calIEvent);
         if (
           ex &&
           cal.dtz.now().compare(ex.startDate || ex.entryDate) < 0 &&
           this.isItemInFilters(ex)
         ) {
           exMatch = ex;
         }
       }, this);