diff --git a/vectors.h b/vectors.h
index 5486046b4..af0f557ec 100644
--- a/vectors.h
+++ b/vectors.h
@@ -16,7 +16,7 @@
 
 // return the the magnitude of a vector
 template <size_t VECDIM>
-[[nodiscard]] [[gnu::const]] constexpr auto vec_len(const std::array<double, VECDIM> vec) -> double {
+[[nodiscard]] constexpr auto vec_len(const std::array<double, VECDIM> &vec) -> double {
   const double squaredlen = std::accumulate(vec.begin(), vec.end(), 0., [](auto a, auto b) { return a + b * b; });
 
   return std::sqrt(squaredlen);