connection.go | 6 ++++++
 misc.go       | 2 ++
 torrent.go    | 8 ++++++++

diff --git a/connection.go b/connection.go
index 6e9fd0288390d28831c4aeb1e0dd2a5d166b144f..cea8dab68b254285aea3eca8142e23d733d79d65 100644
--- a/connection.go
+++ b/connection.go
@@ -498,6 +498,12 @@ 		} else {
 			panic("requesting while choked and not allowed fast")
 		}
 	}
+	if cn.t.hashingPiece(pieceIndex(r.Index)) {
+		panic("piece is being hashed")
+	}
+	if cn.t.pieceQueuedForHash(pieceIndex(r.Index)) {
+		panic("piece is queued for hash")
+	}
 	if cn.requests == nil {
 		cn.requests = make(map[request]struct{})
 	}
diff --git a/misc.go b/misc.go
index 10df12447466360a6715cffd0c775bdab0970122..bab40e1721952fd936e1625d4004e8c41ec44db2 100644
--- a/misc.go
+++ b/misc.go
@@ -168,3 +168,5 @@ 	return ret
 }
 
 var unlimited = rate.NewLimiter(rate.Inf, 0)
+
+type pieceIndex = int
diff --git a/torrent.go b/torrent.go
index fe3df93f4ca125c1f5685f541d757d8bf3c1310c..5736dee5ff7ca891180a499b308014835d9fcf23 100644
--- a/torrent.go
+++ b/torrent.go
@@ -1776,3 +1776,11 @@ func (t *Torrent) allStats(f func(*ConnStats)) {
 	f(&t.stats)
 	f(&t.cl.stats)
 }
+
+func (t *Torrent) hashingPiece(i pieceIndex) bool {
+	return t.pieces[i].hashing
+}
+
+func (t *Torrent) pieceQueuedForHash(i pieceIndex) bool {
+	return t.piecesQueuedForHash.Get(bitmap.BitIndex(i))
+}