diff --git a/mozilla/calendar/base/src/calItemBase.js b/mozilla/calendar/base/src/calItemBase.js
index 4e6befd8682..5f39c09a56a 100644
--- a/mozilla/calendar/base/src/calItemBase.js
+++ b/mozilla/calendar/base/src/calItemBase.js
@@ -415,7 +415,7 @@ calItemBase.prototype = {
         } else {
             this.modify();
         }
-        if (aValue) {
+        if (aValue || !isNaN(aValue)) {
             this.mProperties.setProperty(aName.toUpperCase(), aValue);
         } else {
             this.deleteProperty(aName);