diff --git a/internal/database/fixes/20260608_backfill_anime_duration_seconds.go b/internal/database/fixes/20260608_backfill_anime_duration_seconds.go
new file mode 100644
index 0000000..0180768
--- /dev/null
+++ b/internal/database/fixes/20260608_backfill_anime_duration_seconds.go
@@ -0,0 +1,81 @@
+package fixes
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+	"mal/integrations/jikan"
+	"mal/internal/config"
+	"mal/internal/db"
+	"mal/internal/observability"
+)
+
+func init() {
+	Register(Fix{
+		ID: "20260608_backfill_anime_duration_seconds",
+		Apply: func(ctx context.Context, sqlDB *sql.DB) error {
+			rows, err := sqlDB.QueryContext(ctx, `
+SELECT id, title_original, title_english, title_japanese, image_url, airing
+FROM anime
+WHERE duration_seconds IS NULL;
+`)
+			if err != nil {
+				return fmt.Errorf("query anime rows missing duration_seconds: %w", err)
+			}
+			defer func() { _ = rows.Close() }()
+
+			client := jikan.NewClient(config.Config{}, db.New(sqlDB), observability.NewMetrics())
+
+			type animeRow struct {
+				id            int64
+				titleOriginal string
+			}
+
+			var toUpdate []animeRow
+			for rows.Next() {
+				var row animeRow
+				var titleEnglish sql.NullString
+				var titleJapanese sql.NullString
+				var imageURL string
+				var airing sql.NullBool
+				if err := rows.Scan(
+					&row.id,
+					&row.titleOriginal,
+					&titleEnglish,
+					&titleJapanese,
+					&imageURL,
+					&airing,
+				); err != nil {
+					return fmt.Errorf("scan anime row missing duration_seconds: %w", err)
+				}
+				toUpdate = append(toUpdate, row)
+			}
+			if err := rows.Err(); err != nil {
+				return fmt.Errorf("iterate anime rows missing duration_seconds: %w", err)
+			}
+
+			for _, row := range toUpdate {
+				anime, err := client.GetAnimeByID(ctx, int(row.id))
+				if err != nil {
+					return fmt.Errorf("fetch anime %d for duration backfill: %w", row.id, err)
+				}
+
+				durationSeconds := anime.DurationSeconds()
+				if durationSeconds <= 0 {
+					continue
+				}
+
+				if _, err := sqlDB.ExecContext(
+					ctx,
+					`UPDATE anime SET duration_seconds = ? WHERE id = ? AND duration_seconds IS NULL`,
+					durationSeconds,
+					row.id,
+				); err != nil {
+					return fmt.Errorf("update anime %d duration_seconds: %w", row.id, err)
+				}
+			}
+
+			return nil
+		},
+	})
+}
diff --git a/internal/watchlist/service.go b/internal/watchlist/service.go
index 0d29795..4c2c4e9 100644
--- a/internal/watchlist/service.go
+++ b/internal/watchlist/service.go
@@ -29,13 +29,19 @@ func (s *watchlistService) UpdateEntry(ctx context.Context, userID string, anime
 	return s.repo.InTx(ctx, func(txCtx context.Context, repo domain.WatchlistRepository) error {
 		_, err := repo.GetAnime(txCtx, animeID)
 		if err != nil && fetchErr == nil {
+			durationSeconds := anime.DurationSeconds()
+			duration := sql.NullFloat64{Valid: durationSeconds > 0}
+			if duration.Valid {
+				duration.Float64 = durationSeconds
+			}
 			if _, err := repo.UpsertAnime(txCtx, db.UpsertAnimeParams{
-				ID:            int64(anime.MalID),
-				TitleOriginal: anime.Title,
-				TitleEnglish:  sql.NullString{String: anime.TitleEnglish, Valid: anime.TitleEnglish != ""},
-				TitleJapanese: sql.NullString{String: anime.TitleJapanese, Valid: anime.TitleJapanese != ""},
-				ImageUrl:      anime.ImageURL(),
-				Airing:        sql.NullBool{Bool: anime.Airing, Valid: true},
+				ID:              int64(anime.MalID),
+				TitleOriginal:   anime.Title,
+				TitleEnglish:    sql.NullString{String: anime.TitleEnglish, Valid: anime.TitleEnglish != ""},
+				TitleJapanese:   sql.NullString{String: anime.TitleJapanese, Valid: anime.TitleJapanese != ""},
+				ImageUrl:        anime.ImageURL(),
+				Airing:          sql.NullBool{Bool: anime.Airing, Valid: true},
+				DurationSeconds: duration,
 			}); err != nil {
 				return err
 			}