diff --git a/include/openmc/cell.h b/include/openmc/cell.h
index 8a330060c3..d3b411dda3 100644
--- a/include/openmc/cell.h
+++ b/include/openmc/cell.h
@@ -2,12 +2,14 @@
 #define OPENMC_CELL_H
 
 #include <cstdint>
+#include <functional> // for hash
 #include <limits>
 #include <memory> // for unique_ptr
 #include <string>
 #include <unordered_map>
 #include <vector>
 
+#include <gsl/gsl>
 #include "hdf5.h"
 #include "pugixml.hpp"
 #include "dagmc.h"
@@ -286,10 +288,40 @@ private:
   std::vector<std::vector<int32_t>> partitions_;
 };
 
+//==============================================================================
+//! Define an instance of a particular cell
+//==============================================================================
+
+struct CellInstance {
+  //! Check for equality
+  bool operator==(const CellInstance& other) const
+  { return index_cell == other.index_cell && instance == other.instance; }
+
+  gsl::index index_cell;
+  gsl::index instance;
+};
+} // namespace openmc
+
+namespace std {
+template<>
+struct hash<openmc::CellInstance> {
+  // Taken from https://stackoverflow.com/a/17017281
+  std::size_t operator()(const openmc::CellInstance& k) const
+  {
+    std::size_t res = 17;
+    res = 31 * res + std::hash<gsl::index>()(k.index_cell);
+    res = 31 * res + std::hash<gsl::index>()(k.instance);
+    return res;
+  }
+};
+} // namespace std
+
 //==============================================================================
 // Non-member functions
 //==============================================================================
 
+namespace openmc {
+
 void read_cells(pugi::xml_node node);
 
 #ifdef DAGMC
diff --git a/include/openmc/tallies/filter_cell_instance.h b/include/openmc/tallies/filter_cell_instance.h
index 0895cc1eff..33874b85d6 100644
--- a/include/openmc/tallies/filter_cell_instance.h
+++ b/include/openmc/tallies/filter_cell_instance.h
@@ -2,43 +2,14 @@
 #define OPENMC_TALLIES_FILTER_CELL_INSTANCE_H
 
 #include <cstdint>
-#include <functional> // for hash
 #include <unordered_map>
 #include <vector>
 
 #include <gsl/gsl>
 
+#include "openmc/cell.h"
 #include "openmc/tallies/filter.h"
 
-//==============================================================================
-//! Define an instance of a particular cell
-//==============================================================================
-
-namespace openmc {
-struct CellInstance {
-  //! Check for equality
-  bool operator==(const CellInstance& other) const
-  { return index_cell == other.index_cell && instance == other.instance; }
-
-  gsl::index index_cell;
-  gsl::index instance;
-};
-} // namespace openmc
-
-namespace std {
-template<>
-struct hash<openmc::CellInstance> {
-  // Taken from https://stackoverflow.com/a/17017281
-  std::size_t operator()(const openmc::CellInstance& k) const
-  {
-    std::size_t res = 17;
-    res = 31 * res + std::hash<gsl::index>()(k.index_cell);
-    res = 31 * res + std::hash<gsl::index>()(k.instance);
-    return res;
-  }
-};
-} // namespace std
-
 
 namespace openmc {