diff --git a/failsafeloggers/failsafe_logger.cpp b/failsafeloggers/failsafe_logger.cpp
index 91416e0..f1fcb14 100644
--- a/failsafeloggers/failsafe_logger.cpp
+++ b/failsafeloggers/failsafe_logger.cpp
@@ -8,7 +8,7 @@
 
 void FailsafeLogger::outputFailsafeLog(
     const int64_t zoneId, const bool newFailsafeState,
-    const std::string location, const std::string reason)
+    const std::string& location, const std::string& reason)
 {
     // Remove outdated log entries.
     const auto now = std::chrono::high_resolution_clock::now();
diff --git a/failsafeloggers/failsafe_logger.hpp b/failsafeloggers/failsafe_logger.hpp
index 0e13919..b53e9f2 100644
--- a/failsafeloggers/failsafe_logger.hpp
+++ b/failsafeloggers/failsafe_logger.hpp
@@ -39,8 +39,8 @@
     /** Attempt to output an entering/leaving-failsafe-mode log.
      */
     void outputFailsafeLog(int64_t zoneId, bool newFailsafeState,
-                           const std::string location,
-                           const std::string reason);
+                           const std::string& location,
+                           const std::string& reason);
 
   private:
     // The maximum number of log entries to be output within 1 second.
diff --git a/failsafeloggers/failsafe_logger_utility.hpp b/failsafeloggers/failsafe_logger_utility.hpp
index 05ed3ea..465fcdb 100644
--- a/failsafeloggers/failsafe_logger_utility.hpp
+++ b/failsafeloggers/failsafe_logger_utility.hpp
@@ -24,8 +24,8 @@
  * logs for its corresponding zones.
  */
 inline void outputFailsafeLogWithSensor(
-    const std::string sensorName, const bool newFailsafeState,
-    const std::string location, const std::string reason)
+    const std::string& sensorName, const bool newFailsafeState,
+    const std::string& location, const std::string& reason)
 {
     for (const int64_t zoneId : sensorNameToZoneId[sensorName])
     {
@@ -42,7 +42,7 @@
  */
 inline void outputFailsafeLogWithZone(
     const int64_t zoneId, const bool newFailsafeState,
-    const std::string location, const std::string reason)
+    const std::string& location, const std::string& reason)
 {
     if (zoneIdToFailsafeLogger.count(zoneId))
     {