diff --git a/tape/encode.go b/tape/encode.go
index 8d225f0..7ff0fc5 100644
--- a/tape/encode.go
+++ b/tape/encode.go
@@ -92,7 +92,7 @@ func (this *Encoder) WriteUintN(value uint64, bytes int) (n int, err error) {
 	// TODO: don't make multiple write calls (without allocating)
 	buffer := [1]byte { }
 	for bytesLeft := bytes; bytesLeft > 0; bytesLeft -- {
-		buffer[0] = byte(buffer[0]) >> ((bytesLeft - 1) * 8)
+		buffer[0] = byte(value) >> ((bytesLeft - 1) * 8)
 		nn, err := this.Write(buffer[:])
 		n += nn; if err != nil { return n, err }
 	}