diff --git a/typefactory/typefactory.h b/typefactory/typefactory.h
index 7696432..6f84810 100644
--- a/typefactory/typefactory.h
+++ b/typefactory/typefactory.h
@@ -75,7 +75,7 @@ class TypeFsactory {
      * @endcode
      */
     template<class Derived>
-    void registerType (ClassId_T id) {
+    void registerType (const ClassId_T& id) {
       /// store pointer to constructor of Derived class
       classes[id] = &typefactory<Derived>;
     }
@@ -86,7 +86,7 @@ class TypeFsactory {
      * @return shared pointer to new class.
      * @throws std::our_of_range when id not found in map
      */
-    typefactoryFunction create (ClassId_T id) const {
+    typefactoryFunction create (const ClassId_T& id) const {
       /// constructor of registered type will call here
       return classes.at (id);
     }