reader.go | 2 +-

diff --git a/reader.go b/reader.go
index d1f9d2aaf7b424f762a9217dd941bffdae59dc37..b5eacf5b7d3f2bd9eaf04940c8cdb78fef5b4b61 100644
--- a/reader.go
+++ b/reader.go
@@ -170,7 +170,7 @@ 		}
 		b1 := b[:avail]
 		pi := int(pos / r.t.Info().PieceLength)
 		ip := r.t.Info().Piece(pi)
-		po := pos % ip.Length()
+		po := pos % r.t.Info().PieceLength
 		missinggo.LimitLen(&b1, ip.Length()-po)
 		n, err = r.t.readAt(b1, pos)
 		if n != 0 {