diff --git a/include/openmc/output.h b/include/openmc/output.h
index 6207e2eda..6d6d6ba0f 100644
--- a/include/openmc/output.h
+++ b/include/openmc/output.h
@@ -19,8 +19,9 @@ void header(const char* msg, int level);
 
 
 //==============================================================================
-//! Retrieve a time stamp with the format "yyyy-mm-dd hh:mm:ss"
+//! Retrieve a time stamp
 //!
+//! \return current time stamp (format: "yyyy-mm-dd hh:mm:ss")
 //==============================================================================
 
 std::string time_stamp();
diff --git a/include/openmc/plot.h b/include/openmc/plot.h
index 3cd81d5b4..8b5e6c19a 100644
--- a/include/openmc/plot.h
+++ b/include/openmc/plot.h
@@ -1,7 +1,7 @@
 #ifndef OPENMC_PLOT_H
 #define OPENMC_PLOT_H
 
-#include <map>
+#include <unordered_map>
 #include <sstream>
 
 #include "xtensor/xarray.hpp"
@@ -24,7 +24,7 @@ constexpr int BLUE  = 2;
 
 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 std::unordered_map<int, int> plot_map; //!< map of plot ids to index
 
 extern "C" int32_t n_plots; //!< number of plots in openmc run
 
diff --git a/src/plot.cpp b/src/plot.cpp
index ab8db4e00..ae14ea9df 100644
--- a/src/plot.cpp
+++ b/src/plot.cpp
@@ -24,7 +24,7 @@ namespace openmc {
 
 int PLOT_LEVEL_LOWEST = -1;
 
-std::map<int, int> plot_map;
+std::unordered_map<int, int> plot_map;
 
 int n_plots;
 
diff --git a/src/progress_bar.cpp b/src/progress_bar.cpp
index 444dfa5ed..f412793c9 100644
--- a/src/progress_bar.cpp
+++ b/src/progress_bar.cpp
@@ -48,18 +48,19 @@ ProgressBar::set_value(double val) {
   }
 
   bar.append("% |");
-
   // remaining width of the bar
-  int remain = BAR_WIDTH - bar.size() - 2;
+  int remaining_width = BAR_WIDTH - bar.size() - 2;
   
   // set the bar width
   if (val >= 100.0) {
-    bar.append(remain, '=');
+    bar.append(remaining_width, '=');
+  } else if (val < 0.0) {
+    bar.append(remaining_width, ' ');    
   } else {
-    int width = (int)((double)remain*val/100);
+    int width = (int)((double)remaining_width*val/100);
     bar.append(width, '=');
     bar.append(1, '>');
-    bar.append(remain-width-1, ' ');
+    bar.append(remaining_width-width-1, ' ');
   }
 
   bar.append("|+");