From 91ff6ce2d81c299153d99fe0eba7f4bfa9d742b7 Mon Sep 17 00:00:00 2001
From: hius07 <62179190+hius07@users.noreply.github.com>
Date: Mon, 13 Feb 2023 01:14:49 +0200
Subject: [PATCH] ReaderBookmark: fix comparing positions (#10109)

---
 frontend/apps/reader/modules/readerbookmark.lua | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/frontend/apps/reader/modules/readerbookmark.lua b/frontend/apps/reader/modules/readerbookmark.lua
index 4b83fe6c1..0c602e586 100644
--- a/frontend/apps/reader/modules/readerbookmark.lua
+++ b/frontend/apps/reader/modules/readerbookmark.lua
@@ -245,13 +245,19 @@ function ReaderBookmark:isBookmarkInPositionOrder(a, b)
             if compare_xp then
                 if compare_xp == 0 then -- both bookmarks with the same start
                     if a.highlighted and b.highlighted then -- both are highlights, compare ends
-                        return self.ui.document:compareXPointers(a.pos1, b.pos1) < 0
+                        compare_xp = self.ui.document:compareXPointers(a.pos1, b.pos1)
+                        if compare_xp then
+                            return compare_xp < 0
+                        end
+                        logger.warn("Invalid xpointer in highlight:", a.pos1, b.pos1)
+                        return
                     end
                     return a.highlighted -- have page bookmarks before highlights
                 end
                 return compare_xp < 0
             end
             -- if compare_xp is nil, some xpointer is invalid and will be sorted first to page 1
+            logger.warn("Invalid xpointer in highlight:", a.page, b.page)
         end
         return a_page > b_page
     end