diff --git a/include/openmc/lattice.h b/include/openmc/lattice.h
index 618859c80a..64936ca0a3 100644
--- a/include/openmc/lattice.h
+++ b/include/openmc/lattice.h
@@ -257,7 +257,7 @@ public:
 
   ReverseLatticeIter rbegin();
 
-  bool are_valid_indices(const int i_xyz[3]) const;
+  bool are_valid_indices(array<int, 3> const& i_xyz) const;
 
   std::pair<double, std::array<int, 3>>
   distance(Position r, Direction u, const std::array<int, 3>& i_xyz) const;
diff --git a/include/openmc/particle.h b/include/openmc/particle.h
index e8002cedbf..0aa3f4ac54 100644
--- a/include/openmc/particle.h
+++ b/include/openmc/particle.h
@@ -4,7 +4,6 @@
 //! \file particle.h
 //! \brief Particle type
 
-#include <array>
 #include <cstdint>
 #include <memory> // for unique_ptr
 #include <sstream>
@@ -55,9 +54,7 @@ public:
   int cell {-1};
   int universe {-1};
   int lattice {-1};
-  int lattice_x {-1};
-  int lattice_y {-1};
-  int lattice_z {-1};
+  array<int, 3> lattice_i {-1, -1, -1};
   bool rotated {false};  //!< Is the level rotated?
 };
 
diff --git a/src/geometry.cpp b/src/geometry.cpp
index 23622ebad0..ce6dfd65b0 100644
--- a/src/geometry.cpp
+++ b/src/geometry.cpp
@@ -315,7 +315,7 @@ cross_lattice(Particle& p, const BoundaryInfo& boundary)
   if (settings::verbosity >= 10 || p.trace_) {
     write_message(fmt::format(
       "    Crossing lattice {}. Current position ({},{},{}). r={}",
-      lat.id_, coord.lattice_x, coord.lattice_y, coord.lattice_z, p.r()), 1);
+      lat.id_, coord.lattice_i[0], coord.lattice_i[1], coord.lattice_i[2], p.r()), 1);
   }
 
   // Set the lattice indices.