diff --git a/chrome/content/zotero/xpcom/date.js b/chrome/content/zotero/xpcom/date.js
index 9dd99ae58..d52090917 100644
--- a/chrome/content/zotero/xpcom/date.js
+++ b/chrome/content/zotero/xpcom/date.js
@@ -296,13 +296,13 @@ Zotero.Date = new function(){
 		
 		// Parse 'yesterday'/'today'/'tomorrow'
 		var lc = (string + '').toLowerCase();
-		if (lc == 'yesterday' || (Zotero.getString && lc === Zotero.getString('date.yesterday'))) {
+		if (lc == 'yesterday' || (Zotero.isClient && lc === Zotero.getString('date.yesterday'))) {
 			string = Zotero.Date.dateToSQL(new Date(Date.now() - 1000*60*60*24)).substr(0, 10); // no 'this' for translator sandbox
 		}
-		else if (lc == 'today' || (Zotero.getString && lc == Zotero.getString('date.today'))) {
+		else if (lc == 'today' || (Zotero.isClient && lc == Zotero.getString('date.today'))) {
 			string = Zotero.Date.dateToSQL(new Date()).substr(0, 10);
 		}
-		else if (lc == 'tomorrow' || (Zotero.getString && lc == Zotero.getString('date.tomorrow'))) {
+		else if (lc == 'tomorrow' || (Zotero.isClient && lc == Zotero.getString('date.tomorrow'))) {
 			string = Zotero.Date.dateToSQL(new Date(Date.now() + 1000*60*60*24)).substr(0, 10);
 		}
 		else {