diff --git a/corsika/detail/modules/proposal/ContinuousProcess.inl b/corsika/detail/modules/proposal/ContinuousProcess.inl
index ec0d24d5684487dc3e3e6a73f7c96814a34f71b1..b190619b39b88f0b81ceafbb7fff4a73992d4862 100644
--- a/corsika/detail/modules/proposal/ContinuousProcess.inl
+++ b/corsika/detail/modules/proposal/ContinuousProcess.inl
@@ -75,7 +75,7 @@ namespace corsika::proposal {
         grammage / 1_g * square(1_cm), E_i_total / 1_MeV, E_f_total / 1_MeV, distr(RNG_),
         distr(RNG_));
 
-    auto root = initial_particle_dir.getCoordinateSystem();
+    auto const& root = initial_particle_dir.getCoordinateSystem();
 
     // construct vector that is normal to initial direction.
     DirectionVector normal_vec{root, {0, 0, 0}};