diff --git a/modules/emacs/undo/config.el b/modules/emacs/undo/config.el
index d706ac5c4..e9ed30895 100644
--- a/modules/emacs/undo/config.el
+++ b/modules/emacs/undo/config.el
@@ -21,7 +21,24 @@
               (define-key map (kbd "C-x r U") #'undo-fu-session-recover)
               map)
     :init-value nil
-    :global t))
+    :global t)
+
+  ;; HACK: If undo-tree creates its diff window next to a popup/side window, the
+  ;;   `balance-window' calls in `undo-tree-visualizer-update-diff' can wreck
+  ;;   havoc on the window tree, making the diff window an unclosable "root"
+  ;;   window (which emacs will happily throw errors about when you call
+  ;;   `undo-tree-visualizer-quit'). Breakage ensues.
+  ;; REVIEW: Should be reported/addressed upstream, in undo-tree!
+  (defadvice! +undo-tree--show-visualizer-diff-safely-a (&optional node)
+    :override #'undo-tree-visualizer-show-diff
+    (setq undo-tree-visualizer-diff t)
+    (let ((buff (with-current-buffer undo-tree-visualizer-parent-buffer
+                  (with-current-buffer (undo-tree-diff node)
+                    (hide-mode-line-mode +1))))
+          (display-buffer-mark-dedicated 'soft)
+          (win (split-window (get-buffer-window undo-tree-visualizer-parent-buffer))))
+      (set-window-buffer win buff)
+      (shrink-window-if-larger-than-buffer win))))
 
 
 (use-package! undo-fu-session