diff --git a/pid/zone.cpp b/pid/zone.cpp
index b1da7ec..81425c3 100644
--- a/pid/zone.cpp
+++ b/pid/zone.cpp
@@ -96,12 +96,12 @@
     return _cachedValuesByName.at(name);
 }
 
-void PIDZone::addFanInput(std::string fan)
+void PIDZone::addFanInput(const std::string& fan)
 {
     _fanInputs.push_back(fan);
 }
 
-void PIDZone::addThermalInput(std::string therm)
+void PIDZone::addThermalInput(const std::string& therm)
 {
     _thermalInputs.push_back(therm);
 }
diff --git a/pid/zone.hpp b/pid/zone.hpp
index 6db7b7e..37fcc77 100644
--- a/pid/zone.hpp
+++ b/pid/zone.hpp
@@ -80,8 +80,8 @@
     void addFanPID(std::unique_ptr<Controller> pid);
     void addThermalPID(std::unique_ptr<Controller> pid);
     double getCachedValue(const std::string& name) override;
-    void addFanInput(std::string fan);
-    void addThermalInput(std::string therm);
+    void addFanInput(const std::string& fan);
+    void addThermalInput(const std::string& therm);
 
 #ifdef __TUNING_LOGGING__
     void initializeLog(void);