diff --git a/calendar/base/content/calendar-item-editing.js b/calendar/base/content/calendar-item-editing.js
index e284d72d180..fc512c0cc0e 100644
--- a/calendar/base/content/calendar-item-editing.js
+++ b/calendar/base/content/calendar-item-editing.js
@@ -20,6 +20,7 @@
  *
  * Contributor(s):
  *   Stuart Parmenter <stuart.parmenter@oracle.com>
+ *   Robin Edrenius <robin.edrenius@gmail.com>
  *
  * Alternatively, the contents of this file may be used under the terms of
  * either the GNU General Public License Version 2 or later (the "GPL"), or
@@ -149,7 +150,9 @@ function modifyEventWithDialog(item)
         }
     }
 
-    openEventDialog(item, item.calendar, "modify", onModifyItem);
+    if (item) {
+        openEventDialog(item, item.calendar, "modify", onModifyItem);
+    }
 }
 
 function openEventDialog(calendarItem, calendar, mode, callback)
@@ -204,13 +207,15 @@ function getOccurrenceOrParent(occurrence) {
     var buttonLabel2 = props.GetStringFromName("editRecurSingle");
 
     var flags = promptService.BUTTON_TITLE_IS_STRING * promptService.BUTTON_POS_0 +
-                promptService.BUTTON_TITLE_IS_STRING * promptService.BUTTON_POS_1;
+                promptService.BUTTON_TITLE_CANCEL * promptService.BUTTON_POS_1 +
+                promptService.BUTTON_TITLE_IS_STRING * promptService.BUTTON_POS_2;
 
-    if (promptService.confirmEx(null, promptTitle, promptMessage, flags, 
-                                buttonLabel1, buttonLabel2, null, null, {})) {
-        return occurrence;
-    } else {
-        return occurrence.parentItem;
+    var choice = promptService.confirmEx(null, promptTitle, promptMessage, flags,
+                                         buttonLabel1,null , buttonLabel2, null, {});
+    switch(choice) {
+        case 0: return occurrence.parentItem;
+        case 2: return occurrence;
+        default: return null;
     }
 }
 
diff --git a/calendar/lightning/content/calendar-management.js b/calendar/lightning/content/calendar-management.js
index cbb15c05bc0..09c4948137d 100644
--- a/calendar/lightning/content/calendar-management.js
+++ b/calendar/lightning/content/calendar-management.js
@@ -191,6 +191,9 @@ var ltnCalendarViewController = {
         // if we can modify this thing directly (e.g. just the time changed),
         // then do so; otherwise pop up the dialog
         var itemToEdit = getOccurrenceOrParent(aOccurrence);
+        if (!itemToEdit) {
+            return;
+        }
         if (aNewStartTime && aNewEndTime && !aNewStartTime.isDate && !aNewEndTime.isDate) {
         
             var instance = itemToEdit.clone();
@@ -218,6 +221,9 @@ var ltnCalendarViewController = {
 
     deleteOccurrence: function (aOccurrence) {
         var itemToDelete = getOccurrenceOrParent(aOccurrence);
+        if (!itemToDelete) {
+            return;
+        }
         if (itemToDelete.parentItem != itemToDelete) {
             var event = itemToDelete.parentItem.clone();
             event.recurrenceInfo.removeOccurrenceAt(itemToDelete.recurrenceId);
diff --git a/calendar/resources/content/calendarWindow.js b/calendar/resources/content/calendarWindow.js
index 7d9938e5e3f..220829c013f 100644
--- a/calendar/resources/content/calendarWindow.js
+++ b/calendar/resources/content/calendarWindow.js
@@ -21,6 +21,7 @@
  * Contributor(s): Garth Smedley <garths@oeone.com>
  *                 Mike Potter <mikep@oeone.com>
  *                 Eric Belhaire <belhaire@ief.u-psud.fr>
+ *                 Robin Edrenius <robin.edrenius@gmail.com>
  *
  * Alternatively, the contents of this file may be used under the terms of
  * either the GNU General Public License Version 2 or later (the "GPL"), or
@@ -75,6 +76,9 @@ calViewController.prototype.modifyOccurrence = function (aOccurrence, aNewStartT
     if (aNewStartTime && aNewEndTime && !aNewStartTime.isDate 
         && !aNewEndTime.isDate) {
         var itemToEdit = getOccurrenceOrParent(aOccurrence);
+        if (!itemToEdit) {
+            return;
+        }
         var instance = itemToEdit.clone();
         
         var newStartTime = aNewStartTime;
@@ -100,6 +104,9 @@ calViewController.prototype.modifyOccurrence = function (aOccurrence, aNewStartT
 
 calViewController.prototype.deleteOccurrence = function (aOccurrence) {
     var itemToDelete = getOccurrenceOrParent(aOccurrence);
+    if (!itemToDelete) {
+        return;
+    }
     if (itemToDelete.parentItem != itemToDelete) {
         var event = itemToDelete.parentItem.clone();
         event.recurrenceInfo.removeOccurrenceAt(itemToDelete.recurrenceId);