diff --git a/libsrc/core/hashtable.hpp b/libsrc/core/hashtable.hpp
index 1be25b86..408cec4c 100644
--- a/libsrc/core/hashtable.hpp
+++ b/libsrc/core/hashtable.hpp
@@ -46,7 +46,8 @@ namespace ngcore
   class IVec
   {
     /// data
-    T i[(N>0)?N:1];
+    // T i[(N>0)?N:1];
+    std::array<T,N> i;
 
   public:
     ///
@@ -81,7 +82,7 @@ namespace ngcore
     template <typename ARCHIVE>
     void DoArchive(ARCHIVE& ar)
     {
-      ar.Do(i, N);
+      ar.Do(i.begin(), N);
     }
 
     template <int N2, typename T2>
diff --git a/libsrc/core/ng_mpi.cpp b/libsrc/core/ng_mpi.cpp
index 66355a96..bc0470ef 100644
--- a/libsrc/core/ng_mpi.cpp
+++ b/libsrc/core/ng_mpi.cpp
@@ -164,7 +164,7 @@ void ng_init_mpi() {
       imported_mpi4py = true;
     }
     PyObject* py_src = src.ptr();
-    auto type = Py_TYPE(py_src);
+    [[maybe_unused]] auto type = Py_TYPE(py_src);
     if (PyObject_TypeCheck(py_src, &PyMPIComm_Type)) {
       dst = mpi2ng(*PyMPIComm_Get(py_src));
       return !PyErr_Occurred();