diff -dur old/tagged_argument.hpp new/tagged_argument.hpp
--- old/tagged_argument.hpp	2011-03-15 15:16:02.000000000 +0000
+++ new/tagged_argument.hpp	2011-03-15 15:16:10.000000000 +0000
@@ -120,13 +120,13 @@
     }
 # else
     template <class Default>
-    reference operator[](default_<key_type,Default> const& x) const
+    reference operator[](default_<key_type,Default> const&) const
     {
         return value;
     }
 
     template <class F>
-    reference operator[](lazy_default<key_type,F> const& x) const
+    reference operator[](lazy_default<key_type,F> const&) const
     {
         return value;
     }