diff --git a/libs/util/include/psemek/util/array.hpp b/libs/util/include/psemek/util/array.hpp
index 70ef6bb7..868d33a0 100644
--- a/libs/util/include/psemek/util/array.hpp
+++ b/libs/util/include/psemek/util/array.hpp
@@ -345,6 +345,7 @@ namespace psemek::util
 	std::enable_if_t<detail::is_index_v<Ixs...>, T &>
 		array<T, N>::operator()(Ixs ... ixs)
 	{
+		static_assert(sizeof...(Ixs) == N);
 		dims_type dims{static_cast<std::size_t>(ixs)...};
 		return (*this)(dims);
 	}
@@ -354,6 +355,7 @@ namespace psemek::util
 	std::enable_if_t<detail::is_index_v<Ixs...>, T const &>
 		array<T, N>::operator()(Ixs ... ixs) const
 	{
+		static_assert(sizeof...(Ixs) == N);
 		dims_type dims{static_cast<std::size_t>(ixs)...};
 		return (*this)(dims);
 	}