diff --git a/interleaver/interfaces.go b/interleaver/interfaces.go
index 0535e38..bc4c404 100644
--- a/interleaver/interfaces.go
+++ b/interleaver/interfaces.go
@@ -19,14 +19,13 @@ type (
 	}
 
 	BlocKProducer interface {
-		// Returns next block.
 		// error is NoMoreBlocksErr if it run out of blocks.
-		Next() (Block, error)
+		Next(*Block) error
 		Close() error
 	}
 
 	BlockConsumer interface {
-		Consume(Block) error
+		Consume(*Block) error
 		Close() error
 	}
 )
diff --git a/interleaver/leveldb.go b/interleaver/leveldb.go
index fae0ac0..4941697 100644
--- a/interleaver/leveldb.go
+++ b/interleaver/leveldb.go
@@ -44,7 +44,7 @@ func (ldbc *LevelDBBlockConsumer) Close() error {
 	return nil
 }
 
-func (ldbc *LevelDBBlockConsumer) Consume(block Block) (err error) {
+func (ldbc *LevelDBBlockConsumer) Consume(block *Block) (err error) {
 	var encodedKey []byte
 	if encodedKey, err = ldbc.encoder(ldbc.joiner(block.Coord)); err != nil {
 		return
diff --git a/interleaver/sqlite.go b/interleaver/sqlite.go
index 6ed5f5e..6ca4f1a 100644
--- a/interleaver/sqlite.go
+++ b/interleaver/sqlite.go
@@ -49,7 +49,7 @@ func NewSQLiteBlockProducer(path string, splitter common.KeySplitter) (sbp *SQLi
 	return
 }
 
-func (sbp *SQLiteBlockProducer) Next() (block Block, err error) {
+func (sbp *SQLiteBlockProducer) Next(block *Block) (err error) {
 	if sbp.rows == nil {
 		err = NoMoreBlocksErr
 		return