diff --git a/packfile/reader.go b/packfile/reader.go
index f25c8d5..ec597fb 100644
--- a/packfile/reader.go
+++ b/packfile/reader.go
@@ -71,11 +71,11 @@ func readFileHeader(r io.Reader) (uint32, error) {
 	if buf[0] != 'P' || buf[1] != 'A' || buf[2] != 'C' || buf[3] != 'K' {
 		return 0, errors.New("packfile: read header: incorrect signature")
 	}
-	version := uint32(buf[4])<<24 | uint32(buf[5])<<16 | uint32(buf[6])<<8 | uint32(buf[7])
+	version := ntohl(buf[4:])
 	if version != 2 {
 		return 0, fmt.Errorf("packfile: read header: version is %d (only supports 2)", version)
 	}
-	nobjs := uint32(buf[8])<<24 | uint32(buf[9])<<16 | uint32(buf[10])<<8 | uint32(buf[11])
+	nobjs := ntohl(buf[8:])
 	return nobjs, nil
 }
 
diff --git a/packfile/writer.go b/packfile/writer.go
index 1f7a602..c40509d 100644
--- a/packfile/writer.go
+++ b/packfile/writer.go
@@ -54,15 +54,13 @@ func (w *Writer) init() error {
 	if w.wc.n > 0 {
 		return nil
 	}
-	_, err := w.wc.Write([]byte{
+	fileHeader := []byte{
 		'P', 'A', 'C', 'K',
 		0, 0, 0, 2, // version 2
-		byte(w.nobjs >> 24),
-		byte(w.nobjs >> 16),
-		byte(w.nobjs >> 8),
-		byte(w.nobjs),
-	})
-	if err != nil {
+		0, 0, 0, 0,
+	}
+	htonl(fileHeader[8:], w.nobjs)
+	if _, err := w.wc.Write(fileHeader); err != nil {
 		return fmt.Errorf("packfile: write header: %w", err)
 	}
 	return nil