diff --git a/js/ui/workspaceThumbnail.js b/js/ui/workspaceThumbnail.js
index 7b7bc908e..913ed2329 100644
--- a/js/ui/workspaceThumbnail.js
+++ b/js/ui/workspaceThumbnail.js
@@ -822,7 +822,7 @@ const ThumbnailsBox = new Lang.Class({
             // ... move them down one.
             windows.forEach(function(winActor) {
                 let window = winActor.meta_window;
-                window.change_workspace_by_index(window.get_workspace() + 1, true);
+                window.change_workspace_by_index(window.get_workspace().index() + 1, true);
             });
 
             if (isWindow)