diff --git a/serve.go b/serve.go
index 55327a9..52f2f54 100644
--- a/serve.go
+++ b/serve.go
@@ -364,7 +364,7 @@ requested, other TLS certificates are requested on demand.
 		for _, e := range tmps {
 			if fi, err := e.Info(); err != nil {
 				log.Errorx("stat tmp file", err, mlog.Field("filename", e.Name()))
-			} else if now.Sub(fi.ModTime()) > 7*24*time.Hour {
+			} else if now.Sub(fi.ModTime()) > 7*24*time.Hour && !fi.IsDir() {
 				p := filepath.Join(tmpdir, e.Name())
 				if err := os.Remove(p); err != nil {
 					log.Errorx("removing stale temporary file", err, mlog.Field("path", p))