diff --git a/admin/javascript/LeftAndMain.Preview.js b/admin/javascript/LeftAndMain.Preview.js
index 0d23d18a9..d3cc0f520 100644
--- a/admin/javascript/LeftAndMain.Preview.js
+++ b/admin/javascript/LeftAndMain.Preview.js
@@ -452,9 +452,11 @@
 					// No state available at all.
 					this.setCurrentStateName(null);
 				}
-				
+
 				// Mark url as a preview url so it can get special treatment
-				url += ((url.indexOf('?') === -1) ? '?' : '&') + 'CMSPreview=1';
+				if (url) {
+					url += ((url.indexOf('?') === -1) ? '?' : '&') + 'CMSPreview=1';
+				}
 
 				// If this preview panel isn't visible at the moment, delay loading the URL until it (maybe) is later
 				if (this.is('.column-hidden')) {