diff --git a/include/openmc/plot.h b/include/openmc/plot.h
index 48d486e5d..1beff9ca8 100644
--- a/include/openmc/plot.h
+++ b/include/openmc/plot.h
@@ -24,7 +24,7 @@ extern int PLOT_LEVEL_LOWEST; //!< lower bound on plot universe level
 
 extern std::map<int, int> plot_map; //!< map of plot ids to index
 
-extern int n_plots; //!< number of plots in openmc run
+extern "C" int32_t n_plots; //!< number of plots in openmc run
 
 class Plot;
 extern std::vector<Plot> plots; //!< Plot instance container
@@ -153,11 +153,11 @@ extern "C" void read_plots(pugi::xml_node* plot_node);
 
 //! Create a ppm image for a plot object
 //! \param[in] plot object
-extern "C" void create_ppm(Plot pl);
+void create_ppm(Plot pl);
 
 //! Create an hdf5 voxel file for a plot object
 //! \param[in] plot object
-extern "C" void create_voxel(Plot pl);
+void create_voxel(Plot pl);
 
 
 } // namespace openmc
diff --git a/include/openmc/xml_interface.h b/include/openmc/xml_interface.h
index 104e6ec27..29de8839e 100644
--- a/include/openmc/xml_interface.h
+++ b/include/openmc/xml_interface.h
@@ -9,7 +9,6 @@
 #include "pugixml.hpp"
 #include "xtensor/xarray.hpp"
 #include "xtensor/xadapt.hpp"
-#include "openmc/string_functions.h"
 
 namespace openmc {
 
diff --git a/src/plot.cpp b/src/plot.cpp
index afa2eade7..ebc6c4f75 100644
--- a/src/plot.cpp
+++ b/src/plot.cpp
@@ -204,16 +204,17 @@ Plot::set_output_path(pugi::xml_node plot_node)
 
   if (check_for_node(plot_node, "filename")) {
     filename << get_node_value(plot_node, "filename");
-  } else {
-    switch(type) {
-    case plot_type::slice:
-      filename << ".ppm";
-      break;
-    case plot_type::voxel:
-      filename << ".h5";
-      break;
-    }
   }
+  // add appropriate file extension to name
+  switch(type) {
+  case plot_type::slice:
+    filename << ".ppm";
+    break;
+  case plot_type::voxel:
+    filename << ".h5";
+    break;
+  }
+
   path_plot = filename.str();
 
   // Copy plot pixel size
@@ -972,6 +973,7 @@ void create_voxel(Plot pl)
     // Write to HDF5 dataset
     voxel_write_slice(x, dspace, dset, memspace, &(data[0]));
   }
+  delete p;
 
   voxel_finalize(dspace, dset, memspace);
   file_close(file_id);
diff --git a/src/surface.cpp b/src/surface.cpp
index f535615e8..265a2f02c 100644
--- a/src/surface.cpp
+++ b/src/surface.cpp
@@ -8,7 +8,7 @@
 #include "openmc/error.h"
 #include "openmc/hdf5_interface.h"
 #include "openmc/xml_interface.h"
-
+#include "openmc/string_functions.h"
 
 namespace openmc {
 
diff --git a/src/xml_interface.cpp b/src/xml_interface.cpp
index fa50eb332..93b65521c 100644
--- a/src/xml_interface.cpp
+++ b/src/xml_interface.cpp
@@ -3,6 +3,7 @@
 #include <algorithm>  // for transform
 #include <sstream>
 
+#include "openmc/string_functions.h"
 #include "openmc/error.h"