diff --git a/cmd/mkpkg/main.go b/cmd/mkpkg/main.go
index 4135d127e..07d3dc2ea 100644
--- a/cmd/mkpkg/main.go
+++ b/cmd/mkpkg/main.go
@@ -21,6 +21,9 @@
 // into a map of filePathOnDisk -> filePathInPackage.
 func parseFiles(s string) (map[string]string, error) {
 	ret := map[string]string{}
+	if len(s) == 0 {
+		return ret, nil
+	}
 	for _, f := range strings.Split(s, ",") {
 		fs := strings.Split(f, ":")
 		if len(fs) != 2 {