@@ -158,6 +158,9 @@ func (l *tarexporter) takeLayerReference(id image.ID, imgDescr *imageDescriptor)

 	if os == "" {

 		os = runtime.GOOS

 	}

+	if !system.IsOSSupported(os) {

+		return fmt.Errorf("os %q is not supported", os)

+	}

 	layer, err := l.lss[os].Get(topLayerID)

 	if err != nil {

 		return err