diff --git a/include/sta/Property.hh b/include/sta/Property.hh
index 7e19b15c..ae94d715 100644
--- a/include/sta/Property.hh
+++ b/include/sta/Property.hh
@@ -46,17 +46,16 @@ template<class TYPE>
 class PropertyRegistry
 {
 public:
-  void defineProperty(const std::string property,
-                      std::function<PropertyValue (TYPE object,
-                                                   Sta *sta)> handler);
+  typedef std::function<PropertyValue (TYPE object, Sta *sta)> PropertyHandler;
+  void defineProperty(const std::string &property,
+                      PropertyHandler handler);
   PropertyValue getProperty(TYPE object,
-                            const std::string property,
+                            const std::string &property,
                             const char *type_name,
                             Sta *sta);
 
 private:
-  std::map<const std::string, std::function<PropertyValue (TYPE object,
-                                                           Sta *sta)>> registry_;
+  std::map<std::string, PropertyHandler> registry_;
 };
 
 class Properties
diff --git a/search/Property.cc b/search/Property.cc
index 1613e3ae..308803a9 100644
--- a/search/Property.cc
+++ b/search/Property.cc
@@ -1384,7 +1384,7 @@ Properties::defineProperty(std::string property,
 template<class TYPE>
 PropertyValue
 PropertyRegistry<TYPE>::getProperty(TYPE object,
-                                    const std::string property,
+                                    const std::string &property,
                                     const char *type_name,
                                     Sta *sta)
 
@@ -1398,9 +1398,8 @@ PropertyRegistry<TYPE>::getProperty(TYPE object,
 
 template<class TYPE>
 void
-PropertyRegistry<TYPE>::defineProperty(const std::string property,
-                                       std::function<PropertyValue (TYPE object,
-                                                                    Sta *sta)> handler)
+PropertyRegistry<TYPE>::defineProperty(const std::string &property,
+                                       PropertyHandler handler)
 {
   registry_[property] = handler;
 }