diff --git a/mtreefs.go b/mtreefs.go
index ec69a38..4c1c28a 100644
--- a/mtreefs.go
+++ b/mtreefs.go
@@ -103,7 +103,7 @@ func mtreeFilename(s string) string {
 	for _, c := range []byte(s) {
 		switch {
 		case c == '\\' || c == '#' || c == ' ' || c < 32 || c > 126:
-			b.WriteString(fmt.Sprintf("\\%03o", c))
+			fmt.Fprintf(&b, "\\%03o", c)
 		default:
 			b.WriteByte(c)
 		}
diff --git a/tar.go b/tar.go
index c91f4fc..9bbdafe 100644
--- a/tar.go
+++ b/tar.go
@@ -105,7 +105,7 @@ func tar(ctx context.Context, enc FormatEncoder, fs *fsBufReader, f *File) (n in
 			}
 
 			// End of the current dir?
-			if !(path.Dir(f.Path) == dir) {
+			if path.Dir(f.Path) != dir {
 				fs.Buffer(f)
 				break
 			}