diff --git a/CMakeLists.txt b/CMakeLists.txt
index e76ed9a9e..bb5c45c42 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -426,7 +426,7 @@ add_library(libopenmc SHARED
   src/simulation.cpp
   src/source.cpp
   src/state_point.cpp
-  src/string_functions.cpp
+  src/string_utils.cpp
   src/summary.cpp
   src/surface.cpp
   src/tallies/filter.cpp
diff --git a/include/openmc/string_functions.h b/include/openmc/string_functions.h
deleted file mode 100644
index a653d1e77..000000000
--- a/include/openmc/string_functions.h
+++ /dev/null
@@ -1,20 +0,0 @@
-//! \file string_functions.h
-//! A collection of helper routines for C-strings and STL strings
-
-#ifndef OPENMC_STRING_FUNCTIONS_H
-#define OPENMC_STRING_FUNCTIONS_H
-
-#include <string>
-
-namespace openmc {
-
-std::string& strtrim(std::string& s);
-
-char* strtrim(char* c_str);
-
-void to_lower(std::string& str);
-
-int word_count(std::string const& str);
-
-} // namespace openmc
-#endif // STRING_FUNCTIONS_H
diff --git a/include/openmc/string_utils.h b/include/openmc/string_utils.h
index 73b1a28ec..35c25e548 100644
--- a/include/openmc/string_utils.h
+++ b/include/openmc/string_utils.h
@@ -1,49 +1,24 @@
 #ifndef OPENMC_STRING_UTILS_H
 #define OPENMC_STRING_UTILS_H
 
-#include <algorithm>
 #include <string>
 #include <vector>
 
 namespace openmc {
 
-inline std::vector<std::string>
-split(const std::string& in)
-{
-  std::vector<std::string> out;
+std::string& strtrim(std::string& s);
 
-  for (int i = 0; i < in.size(); ) {
-    // Increment i until we find a non-whitespace character.
-    if (std::isspace(in[i])) {
-      i++;
+char* strtrim(char* c_str);
 
-    } else {
-      // Find the next whitespace character at j.
-      int j = i + 1;
-      while (j < in.size() && std::isspace(in[j]) == 0) {j++;}
+void to_lower(std::string& str);
 
-      // Push-back everything between i and j.
-      out.push_back(in.substr(i, j-i));
-      i = j + 1; // j is whitespace so leapfrog to j+1
-    }
-  }
+int word_count(std::string const& str);
 
-  return out;
-}
+std::vector<std::string> split(const std::string& in);
 
-inline bool
-ends_with(const std::string& value, const std::string& ending)
-{
-  if (ending.size() > value.size()) return false;
-  return std::equal(ending.rbegin(), ending.rend(), value.rbegin());
-}
+bool ends_with(const std::string& value, const std::string& ending);
 
-inline bool
-starts_with(const std::string& value, const std::string& beginning)
-{
-  if (beginning.size() > value.size()) return false;
-  return std::equal(beginning.begin(), beginning.end(), value.begin());
-}
+bool starts_with(const std::string& value, const std::string& beginning);
 
 } // namespace openmc
 #endif // OPENMC_STRING_UTILS_H
diff --git a/src/cross_sections.cpp b/src/cross_sections.cpp
index aca46a5b9..dbfe41679 100644
--- a/src/cross_sections.cpp
+++ b/src/cross_sections.cpp
@@ -5,7 +5,6 @@
 #include "openmc/error.h"
 #include "openmc/file_utils.h"
 #include "openmc/settings.h"
-#include "openmc/string_functions.h"
 #include "openmc/string_utils.h"
 #include "openmc/xml_interface.h"
 
diff --git a/src/dagmc.cpp b/src/dagmc.cpp
index d4e113977..7c1127867 100644
--- a/src/dagmc.cpp
+++ b/src/dagmc.cpp
@@ -1,7 +1,7 @@
 
 #include "openmc/dagmc.h"
 #include "openmc/error.h"
-#include "openmc/string_functions.h"
+#include "openmc/string_utils.h"
 #include "openmc/settings.h"
 #include "openmc/geometry.h"
 
diff --git a/src/mgxs.cpp b/src/mgxs.cpp
index 1b6e85ffb..8c14f324e 100644
--- a/src/mgxs.cpp
+++ b/src/mgxs.cpp
@@ -17,7 +17,7 @@
 #include "openmc/error.h"
 #include "openmc/math_functions.h"
 #include "openmc/random_lcg.h"
-#include "openmc/string_functions.h"
+#include "openmc/string_utils.h"
 
 
 namespace openmc {
diff --git a/src/plot.cpp b/src/plot.cpp
index 7b0cddb63..9a8aba139 100644
--- a/src/plot.cpp
+++ b/src/plot.cpp
@@ -9,7 +9,7 @@
 #include "openmc/geometry.h"
 #include "openmc/cell.h"
 #include "openmc/material.h"
-#include "openmc/string_functions.h"
+#include "openmc/string_utils.h"
 #include "openmc/mesh.h"
 #include "openmc/output.h"
 #include "openmc/hdf5_interface.h"
diff --git a/src/string_functions.cpp b/src/string_functions.cpp
deleted file mode 100644
index 27e14c9ba..000000000
--- a/src/string_functions.cpp
+++ /dev/null
@@ -1,40 +0,0 @@
-#include "openmc/string_functions.h"
-#include <sstream>
-
-namespace openmc {
-
-std::string& strtrim(std::string& s)
-{
-  const char* t = " \t\n\r\f\v";
-  s.erase(s.find_last_not_of(t) + 1);
-  s.erase(0, s.find_first_not_of(t));
-  return s;
-}
-
-
-char* strtrim(char* c_str)
-{
-  std::string std_str;
-  std_str.assign(c_str);
-  strtrim(std_str);
-  int length = std_str.copy(c_str, std_str.size());
-  c_str[length] = '\0';
-  return c_str;
-}
-
-
-void to_lower(std::string& str)
-{
-  for (int i = 0; i < str.size(); i++) str[i] = std::tolower(str[i]);
-}
-
-int word_count(std::string const& str)
-{
-  std::stringstream stream(str);
-  std::string dum;
-  int count = 0;
-  while (stream >> dum) {count++;}
-  return count;
-}
-
-} // namespace openmc
diff --git a/src/string_utils.cpp b/src/string_utils.cpp
new file mode 100644
index 000000000..c1a203e48
--- /dev/null
+++ b/src/string_utils.cpp
@@ -0,0 +1,78 @@
+#include "openmc/string_utils.h"
+
+#include <algorithm> // for equal
+#include <cctype>    // for tolower, isspace
+#include <sstream>
+
+namespace openmc {
+
+std::string& strtrim(std::string& s)
+{
+  const char* t = " \t\n\r\f\v";
+  s.erase(s.find_last_not_of(t) + 1);
+  s.erase(0, s.find_first_not_of(t));
+  return s;
+}
+
+
+char* strtrim(char* c_str)
+{
+  std::string std_str;
+  std_str.assign(c_str);
+  strtrim(std_str);
+  int length = std_str.copy(c_str, std_str.size());
+  c_str[length] = '\0';
+  return c_str;
+}
+
+
+void to_lower(std::string& str)
+{
+  for (int i = 0; i < str.size(); i++) str[i] = std::tolower(str[i]);
+}
+
+int word_count(std::string const& str)
+{
+  std::stringstream stream(str);
+  std::string dum;
+  int count = 0;
+  while (stream >> dum) {count++;}
+  return count;
+}
+
+std::vector<std::string> split(const std::string& in)
+{
+  std::vector<std::string> out;
+
+  for (int i = 0; i < in.size(); ) {
+    // Increment i until we find a non-whitespace character.
+    if (std::isspace(in[i])) {
+      i++;
+
+    } else {
+      // Find the next whitespace character at j.
+      int j = i + 1;
+      while (j < in.size() && std::isspace(in[j]) == 0) {j++;}
+
+      // Push-back everything between i and j.
+      out.push_back(in.substr(i, j-i));
+      i = j + 1; // j is whitespace so leapfrog to j+1
+    }
+  }
+
+  return out;
+}
+
+bool ends_with(const std::string& value, const std::string& ending)
+{
+  if (ending.size() > value.size()) return false;
+  return std::equal(ending.rbegin(), ending.rend(), value.rbegin());
+}
+
+bool starts_with(const std::string& value, const std::string& beginning)
+{
+  if (beginning.size() > value.size()) return false;
+  return std::equal(beginning.begin(), beginning.end(), value.begin());
+}
+
+} // namespace openmc
diff --git a/src/surface.cpp b/src/surface.cpp
index 265a2f02c..66217a58b 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"
+#include "openmc/string_utils.h"
 
 namespace openmc {