std::addressof isn't available until g++ 4.6.

asio/include/asio/detail/config.hpp

diff --git a/asio/include/asio/detail/config.hpp b/asio/include/asio/detail/config.hpp
index 2aae990..e259916 100644
--- a/asio/include/asio/detail/config.hpp
+++ b/asio/include/asio/detail/config.hpp
@@ -468,11 +468,11 @@
 #   endif // (__cplusplus >= 201103)
 #  endif // defined(__clang__)
 #  if defined(__GNUC__)
-#   if ((__GNUC__ == 4) && (__GNUC_MINOR__ >= 5)) || (__GNUC__ > 4)
+#   if ((__GNUC__ == 4) && (__GNUC_MINOR__ >= 6)) || (__GNUC__ > 4)
 #    if defined(__GXX_EXPERIMENTAL_CXX0X__)
 #     define ASIO_HAS_STD_ADDRESSOF 1
 #    endif // defined(__GXX_EXPERIMENTAL_CXX0X__)
-#   endif // ((__GNUC__ == 4) && (__GNUC_MINOR__ >= 5)) || (__GNUC__ > 4)
+#   endif // ((__GNUC__ == 4) && (__GNUC_MINOR__ >= 6)) || (__GNUC__ > 4)
 #  endif // defined(__GNUC__)
 #  if defined(ASIO_MSVC)
 #   if (_MSC_VER >= 1700)