diff --git a/src/app.cpp b/src/app.cpp
index c9d75aa..58cb7ac 100644
--- a/src/app.cpp
+++ b/src/app.cpp
@@ -134,7 +134,7 @@ Wt::WLocale App::determineLocaleFromBrowser() const {
 
     // 1. Expliziter URL-Parameter ?lang=... hat Vorrang (z.B. de, de-DE, en, en-US, fr, es, it, tl, ja, zh, th)
     if (const auto *langParam = env_.getParameter("lang")) {
-        auto localeName = mapLanguageTag(langParam->toUTF8());
+        auto localeName = mapLanguageTag(*langParam);
         if (!localeName.empty()) {
             return makeLocale(localeName);
         }