diff --git a/CMakeLists.txt b/CMakeLists.txt
index ab52510499..8c67728340 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -437,6 +437,7 @@ set(LIBOPENMC_CXX_SRC
   src/initialize.cpp
   src/hdf5_interface.h
   src/hdf5_interface.cpp
+  src/message_passing.cpp
   src/random_lcg.cpp
   src/random_lcg.h
   src/simulation.cpp
diff --git a/include/openmc.h b/include/openmc.h
index 85cb09a918..1788fb8cca 100644
--- a/include/openmc.h
+++ b/include/openmc.h
@@ -4,9 +4,6 @@
 #include <stdint.h>
 #include <stdbool.h>
 
-#ifdef OPENMC_MPI
-#include "mpi.h"
-#endif
 
 #ifdef __cplusplus
 extern "C" {
@@ -150,11 +147,6 @@ extern "C" {
   extern bool openmc_simulation_initialized;
   extern int openmc_verbosity;
 
-#ifdef OPENMC_MPI
-  // MPI variables
-  extern MPI_Comm openmc_intracomm;
-#endif
-
   // Run modes
   constexpr int RUN_MODE_FIXEDSOURCE {1};
   constexpr int RUN_MODE_EIGENVALUE {2};
diff --git a/src/hdf5_interface.cpp b/src/hdf5_interface.cpp
index b31bf8c1ac..cbbd7d7c3e 100644
--- a/src/hdf5_interface.cpp
+++ b/src/hdf5_interface.cpp
@@ -9,7 +9,7 @@
 #include "hdf5_hl.h"
 #ifdef OPENMC_MPI
 #include "mpi.h"
-#include "openmc.h"
+#include "message_passing.h"
 #endif
 #include "error.h"
 
@@ -163,7 +163,7 @@ file_open(const char* filename, char mode, bool parallel)
   if (parallel) {
     // Setup file access property list with parallel I/O access
     plist = H5Pcreate(H5P_FILE_ACCESS);
-    H5Pset_fapl_mpio(plist, openmc_intracomm, MPI_INFO_NULL);
+    H5Pset_fapl_mpio(plist, openmc::mpi::intracomm, MPI_INFO_NULL);
   }
 #endif
 
diff --git a/src/initialize.cpp b/src/initialize.cpp
index 029a4155d8..4f3261dad7 100644
--- a/src/initialize.cpp
+++ b/src/initialize.cpp
@@ -1,17 +1,15 @@
 #include "openmc.h"
 
-#ifdef OPENMC_MPI
-MPI_Comm openmc_intracomm;
-#endif
+#include "message_passing.h"
 
 
 int
 openmc_init(const void* intracomm)
 {
 #ifdef OPENMC_MPI
-  openmc_intracomm = *static_cast<const MPI_Comm *>(intracomm);
+  openmc::mpi::intracomm = *static_cast<const MPI_Comm *>(intracomm);
 
-  MPI_Fint fcomm = MPI_Comm_c2f(openmc_intracomm);
+  MPI_Fint fcomm = MPI_Comm_c2f(openmc::mpi::intracomm);
   openmc_init_f(&fcomm);
 #else
   openmc_init_f(nullptr);
diff --git a/src/message_passing.cpp b/src/message_passing.cpp
new file mode 100644
index 0000000000..3ab96ffd87
--- /dev/null
+++ b/src/message_passing.cpp
@@ -0,0 +1,15 @@
+#include "message_passing.h"
+
+namespace openmc {
+namespace mpi {
+
+int rank;
+int n_procs;
+
+#ifdef OPENMC_MPI
+MPI_Comm intracomm;
+MPI_Datatype bank;
+#endif
+
+} // namespace mpi
+} // namespace openmc
diff --git a/src/message_passing.h b/src/message_passing.h
new file mode 100644
index 0000000000..fea092c618
--- /dev/null
+++ b/src/message_passing.h
@@ -0,0 +1,18 @@
+#ifndef MESSAGE_PASSING_H
+#define MESSAGE_PASSING_H
+
+namespace openmc {
+namespace mpi {
+
+  extern int rank;
+  extern int n_procs;
+
+#ifdef OPENMC_MPI
+  extern MPI_Datatype bank;
+  extern MPI_Comm intracomm;
+#endif
+
+} // namespace mpi
+} // namespace openmc
+
+#endif // MESSAGE_PASSING_H