diff --git a/Cantera/src/base/ctml.cpp b/Cantera/src/base/ctml.cpp
index 99976b16c..228d519b8 100755
--- a/Cantera/src/base/ctml.cpp
+++ b/Cantera/src/base/ctml.cpp
@@ -78,8 +78,8 @@ namespace ctml {
    *   @param typeString    String type. This is an optional parameter. The default
    *                        is to have an empty string.
    */
-    void addInteger(XML_Node& node, const string &title, const int val, 
-                    const std::string &units, const std::string &type) {
+    void addInteger(XML_Node& node, const std::string &title, const int val, 
+                    const std::string units, const std::string type) {
         XML_Node& f = node.addChild("integer",val);
         f.addAttribute("title",title);
         if (type != "") f.addAttribute("type",type);
diff --git a/Cantera/src/base/ctml.h b/Cantera/src/base/ctml.h
index 173aba2f3..24d536813 100755
--- a/Cantera/src/base/ctml.h
+++ b/Cantera/src/base/ctml.h
@@ -73,8 +73,8 @@ namespace ctml {
    *       typeString should be codified as to its usage.
    */
   void addInteger(Cantera::XML_Node& node, const std::string &titleString, 
-		  const int value, const std::string &unitsString="", 
-		  const std::string &typeString="");
+		  const int value, const std::string unitsString="", 
+		  const std::string typeString="");
 
   void addFloat(Cantera::XML_Node& node, 
 		std::string title,