diff -r 3c00344f49c9 -r f179aa1045a4 lemon/concepts/path.h
--- a/lemon/concepts/path.h	Wed Oct 17 19:14:07 2018 +0200
+++ b/lemon/concepts/path.h	Thu Nov 01 11:27:05 2018 +0100
@@ -70,7 +70,9 @@
 
       /// \brief Template copy constructor
       template <typename CPath>
-      Path(const CPath& cpath) {}
+      Path(const CPath& cpath) {
+        ::lemon::ignore_unused_variable_warning(cpath);
+      }
 
       /// \brief Template assigment operator
       template <typename CPath>