In main.go made use of handler's Error func and in Error() func added missing WriteHeader().

cmd/dwelling-home/main.go

@@ -54,8 +54,7 @@ func main() {
 	r := httpr.New()
 
 	r.NotFoundHandler = func(w http.ResponseWriter, r *http.Request) {
-		w.WriteHeader(http.StatusNotFound)
-		web.ErrorXXX("/ Not Found", "", "", r.Referer(), http.StatusNotFound, w)
+		dwhttp.Error(w, http.StatusNotFound, "", "", r.Referer())
 	}
 
 	r.ServeStatic("/assets/*filepath", web.Assets())

internal/http/web_handlers.go

@@ -188,6 +188,7 @@ func SitemapXml(w http.ResponseWriter, r *http.Request) {
 }
 
 func Error(w http.ResponseWriter, code int, reason, message, referer string) {
+	w.WriteHeader(code)
 	web.ErrorXXX("/ "+http.StatusText(code), reason, message, referer, code, w)
 }