diff --git a/http.go b/http.go
index b7ee9598..88280c44 100644
--- a/http.go
+++ b/http.go
@@ -156,7 +156,7 @@ func (ln tcpKeepAliveListener) Accept() (c net.Conn, err error) {
 func redirectToHTTPS(opts *Options, h http.Handler) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		proto := r.Header.Get("X-Forwarded-Proto")
-		if opts.ForceHTTPS && r.TLS == nil && strings.ToLower(proto) != "https" {
+		if opts.ForceHTTPS && (r.TLS == nil || (proto != "" && strings.ToLower(proto) != "https")) {
 			http.Redirect(w, r, opts.HTTPSAddress, http.StatusPermanentRedirect)
 		}