diff --git a/vectors.h b/vectors.h
index a4b67e650..39014eb9a 100644
--- a/vectors.h
+++ b/vectors.h
@@ -6,7 +6,6 @@
 #include <array>
 #include <cmath>
 #include <numeric>
-#include <span>
 #include <tuple>
 
 #include "constants.h"
@@ -39,7 +38,7 @@ template <size_t S1, size_t S2>
 }
 
 // Get velocity vector of the flow at a position with homologous expansion.
-[[nodiscard]] constexpr auto get_velocity(std::span<const double, 3> x, const double t) -> std::array<double, 3> {
+[[nodiscard]] constexpr auto get_velocity(const std::array<double, 3> &x, const double t) -> std::array<double, 3> {
   return std::array<double, 3>{x[0] / t, x[1] / t, x[2] / t};
 }
 
@@ -127,7 +126,7 @@ template <size_t S1, size_t S2>
   return dopplerfactorsq;
 }
 
-[[nodiscard]] constexpr auto doppler_packet_nucmf_on_nurf(const std::span<const double, 3> &pos_rf,
+[[nodiscard]] constexpr auto doppler_packet_nucmf_on_nurf(const std::array<double, 3> &pos_rf,
                                                           const std::array<double, 3> &dir_rf,
                                                           const double prop_time) -> double {
   return doppler_nucmf_on_nurf(dir_rf, get_velocity(pos_rf, prop_time));