diff --git a/tape/tag.go b/tape/tag.go
index 103f01b..19683e8 100644
--- a/tape/tag.go
+++ b/tape/tag.go
@@ -78,6 +78,6 @@ func bufferLenTag(length int) Tag {
 	if length < int(CNLimit) {
 		return SBA.WithCN(length)
 	} else {
-		return LBA.WithCN(IntBytes(uint64(length)))
+		return LBA.WithCN(IntBytes(uint64(length)) - 1)
 	}
 }