diff --git a/block.go b/block.go
index 0eb78ec..5d06c4a 100644
--- a/block.go
+++ b/block.go
@@ -56,8 +56,8 @@ func (b *Block) Bytes() ([]byte, error) {
 	}
 
 	// Serialize the MsgBlock.
-	var w bytes.Buffer
-	err := b.msgBlock.Serialize(&w)
+	w := bytes.NewBuffer(make([]byte, 0, b.msgBlock.SerializeSize()))
+	err := b.msgBlock.Serialize(w)
 	if err != nil {
 		return nil, err
 	}