diff --git a/chrome/content/zotero/xpcom/data/items.js b/chrome/content/zotero/xpcom/data/items.js
index e55a298726..5afa6a9f9f 100644
--- a/chrome/content/zotero/xpcom/data/items.js
+++ b/chrome/content/zotero/xpcom/data/items.js
@@ -1455,7 +1455,7 @@ Zotero.Items = function() {
 	
 	
 	this.getSortTitle = function(title) {
-		if (title === false || title === undefined) {
+		if (title === false || title === undefined || title == null) {
 			return '';
 		}
 		if (typeof title == 'number') {