diff --git a/src/mgxs_interface.cpp b/src/mgxs_interface.cpp
index 936eeb31f..7ad07d0c9 100644
--- a/src/mgxs_interface.cpp
+++ b/src/mgxs_interface.cpp
@@ -3,6 +3,8 @@
 #include <string>
 #include <unordered_set>
 
+#include <fmt/format.h>
+
 #include "openmc/cell.h"
 #include "openmc/cross_sections.h"
 #include "openmc/container_util.h"
@@ -57,8 +59,7 @@ void MgxsInterface::init()
   // Check if MGXS Library exists
   if (!file_exists(cross_sections_path_)) {
     // Could not find MGXS Library file
-    fatal_error("Cross sections HDF5 file '" + cross_sections_path_ +
-      "' does not exist.");
+    fatal_error(fmt::format("Cross sections HDF5 file '{}' does not exist!", cross_sections_path_));
   }
 
   write_message("Loading cross section data...", 5);
@@ -98,15 +99,14 @@ void
 MgxsInterface::add_mgxs(hid_t file_id, const std::string& name,
   const std::vector<double>& temperature)
 {
-  write_message("Loading " + std::string(name) + " data...", 6);
+  write_message(fmt::format("Loading {} data...", name), 6);
 
   // Check to make sure cross section set exists in the library
   hid_t xs_grp;
   if (object_exists(file_id, name.c_str())) {
     xs_grp = open_group(file_id, name.c_str());
   } else {
-    fatal_error("Data for " + std::string(name) + " does not exist in "
-                + "provided MGXS Library");
+    fatal_error(fmt::format("Data for {} does not exist in provided MGXS Library", name));
   }
 
   nuclides_.emplace_back(xs_grp, temperature, num_energy_groups_,
@@ -187,8 +187,7 @@ void MgxsInterface::read_header(const std::string& path_cross_sections)
   // Check if MGXS Library exists
   if (!file_exists(cross_sections_path_)) {
     // Could not find MGXS Library file
-    fatal_error("Cross sections HDF5 file '" + cross_sections_path_ +
-      "' does not exist.");
+    fatal_error(fmt::format("Cross section HDF5 file '{}' does not exist", cross_sections_path_));
   }
   write_message("Reading cross sections HDF5 file...", 5);
 
diff --git a/src/particle.cpp b/src/particle.cpp
index ae75d91b4..3916eacba 100644
--- a/src/particle.cpp
+++ b/src/particle.cpp
@@ -410,7 +410,7 @@ Particle::cross_surface()
   // TODO: off-by-one
   const auto& surf {model::surfaces[i_surface - 1].get()};
   if (settings::verbosity >= 10 || trace_) {
-    write_message("    Crossing surface " + std::to_string(surf->id_));
+    write_message(fmt::format("    Crossing surface {}", surf->id_));
   }
 
   if (surf->bc_ == Surface::BoundaryType::VACUUM && (settings::run_mode != RunMode::PLOTTING)) {
@@ -437,7 +437,7 @@ Particle::cross_surface()
 
     // Display message
     if (settings::verbosity >= 10 || trace_) {
-      write_message("    Leaked out of surface " + std::to_string(surf->id_));
+      write_message(fmt::format("    Leaked out of surface {}", surf->id_));
     }
     return;
 
@@ -502,7 +502,7 @@ Particle::cross_surface()
 
     // Diagnostic message
     if (settings::verbosity >= 10 || trace_) {
-      write_message("    Reflected from surface " + std::to_string(surf->id_));
+      write_message(fmt::format("    Reflected from surface {}", surf->id_));
     }
     return;
 
@@ -556,8 +556,8 @@ Particle::cross_surface()
 
     // Diagnostic message
     if (settings::verbosity >= 10 || trace_) {
-      write_message("    Hit periodic boundary on surface " +
-        std::to_string(surf->id_));
+      write_message(fmt::format("    Hit periodic boundary on surface {}",
+        surf->id_));
     }
     return;
   }
diff --git a/src/plot.cpp b/src/plot.cpp
index e2fe5abde..267810712 100644
--- a/src/plot.cpp
+++ b/src/plot.cpp
@@ -114,7 +114,7 @@ void read_plots_xml()
   // Check if plots.xml exists
   std::string filename = settings::path_input + "plots.xml";
   if (!file_exists(filename)) {
-    fatal_error("Plots XML file '" + filename + "' does not exist!");
+    fatal_error(fmt::format("Plots XML file '{}' does not exist!", filename));
   }
 
   write_message("Reading plot XML file...", 5);
diff --git a/src/simulation.cpp b/src/simulation.cpp
index 1b39c1329..92cee64cd 100644
--- a/src/simulation.cpp
+++ b/src/simulation.cpp
@@ -33,6 +33,8 @@
 #include <mpi.h>
 #endif
 
+#include <fmt/format.h>
+
 #include <algorithm>
 #include <cmath>
 #include <string>
@@ -500,7 +502,7 @@ void initialize_history(Particle& p, int64_t index_source)
 
   // Display message if high verbosity or trace is on
   if (settings::verbosity >= 9 || p.trace_) {
-    write_message("Simulating Particle " + std::to_string(p.id_));
+    write_message(fmt::format("Simulating Particle {}", p.id_));
   }
 
   // Add paricle's starting weight to count for normalizing tallies later