diff --git a/sys/cpp11-compat/include/riot/mutex.hpp b/sys/cpp11-compat/include/riot/mutex.hpp
index a7ed42de88..ca808cc9db 100644
--- a/sys/cpp11-compat/include/riot/mutex.hpp
+++ b/sys/cpp11-compat/include/riot/mutex.hpp
@@ -44,7 +44,7 @@ class mutex {
  public:
   using native_handle_type = mutex_t*;
 
-  inline constexpr mutex() noexcept : m_mtx{0} {}
+  inline constexpr mutex() noexcept : m_mtx{{0}} {}
   ~mutex();
 
   void lock();