Index: src/js/media/views/attachments/browser.js
===================================================================
--- src/js/media/views/attachments/browser.js	(revision 52649)
+++ src/js/media/views/attachments/browser.js	(working copy)
@@ -130,7 +130,7 @@
 			mediaFoundHasMoreResultsMessage = __( 'Number of media items displayed: %d. Scroll the page for more results.' );
 		}
 
-		if ( this.collection.mirroring.args.s ) {
+		if (this.collection.hasOwnProperty('mirroring') && this.collection.mirroring.args.s) {
 			count = this.collection.length;
 
 			if ( 0 === count ) {