diff --git a/lemon/concepts/path.h b/lemon/concepts/path.h
--- a/lemon/concepts/path.h
+++ b/lemon/concepts/path.h
@@ -168,6 +168,7 @@
           ignore_unused_variable_warning(ed);
         }
         _Path& p;
+        PathDumperConstraints() {}
       };
 
       template <typename _Digraph, typename _Path>
@@ -193,6 +194,7 @@
           ignore_unused_variable_warning(ed);
         }
         _Path& p;
+        PathDumperConstraints() {}
       };
 
     }