diff --git a/static/js/Wiki.js b/static/js/Wiki.js
index f0c8dcc..a8f058e 100644
--- a/static/js/Wiki.js
+++ b/static/js/Wiki.js
@@ -1498,7 +1498,7 @@ Wiki.prototype.update_editor_revisions = function ( result, editor ) {
     } );
     this.display_error(
       'Your changes to the note titled "' + editor.title +
-      '" have overwritten changes made in another window by ' + result.previous_revision.username + '.',
+      '" have overwritten changes made in another window by ' + ( result.previous_revision.username || 'you' ) + '.',
       [ compare_button ], editor.iframe
     );