diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9dc48ef54..348d412f9 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -43,6 +43,7 @@ The format is a modified version of [Keep a Changelog](https://keepachangelog.co
 - Fixed library entries without a date added getting their last update time as date added when updating from v0.20.x ([@AntsyLich](https://github.com/AntsyLich))
 - Fixed the app closing when WebView's page process crashed ([@AntsyLich](https://github.com/AntsyLich))
 - Fixed installing or updating an extension sometimes cancelling the install of another one ([@AntsyLich](https://github.com/AntsyLich))
+- Fixed updating from v0.20.x taking up to hours on libraries with many duplicate entries ([@AntsyLich](https://github.com/AntsyLich))
 
 ## [v0.21.0] - 2026-10-12
 ### Added
diff --git a/data/src/main/sqldelight/tachiyomi/migrations/17.sqm b/data/src/main/sqldelight/tachiyomi/migrations/17.sqm
index b0d945b5d..55bd90652 100644
--- a/data/src/main/sqldelight/tachiyomi/migrations/17.sqm
+++ b/data/src/main/sqldelight/tachiyomi/migrations/17.sqm
@@ -31,6 +31,9 @@ WHERE (source, url) IN (
     HAVING count(*) > 1
 );
 
+-- Moving the chapters looks each one's entry up here, which without an index scans the whole table per chapter
+CREATE INDEX duplicate_mangas_id_index ON duplicate_mangas(_id);
+
 UPDATE mangas
 SET favorite_at = merged.favorite_at,
     initialized = merged.initialized,