diff --git a/src/physics.cpp b/src/physics.cpp
index 26b3a3520..0df8e63c0 100644
--- a/src/physics.cpp
+++ b/src/physics.cpp
@@ -345,12 +345,14 @@ void sample_photon_reaction(Particle& p)
 
   // Photoelectric effect
   double prob_after = prob + micro.photoelectric;
-  int i_grid = micro.index_grid;
-  double f = micro.interp_factor;
-  const auto& xs_lower = xt::row(element.cross_sections_, i_grid);
-  const auto& xs_upper = xt::row(element.cross_sections_, i_grid + 1);
 
   if (prob_after > cutoff) {
+
+    int i_grid = micro.index_grid;
+    double f = micro.interp_factor;
+    const auto& xs_lower = xt::row(element.cross_sections_, i_grid);
+    const auto& xs_upper = xt::row(element.cross_sections_, i_grid + 1);
+
     for (int i_shell = 0; i_shell < element.shells_.size(); ++i_shell) {
       const auto& shell {element.shells_[i_shell]};