[boost] [Proto][MPL]Missing ADL barrier in MPL

I've just hit a spurrious ADL resolution using MPL and Proto. I made a new function called size that took a proto expression and I get the compiler to complain about ambiguity between mpl::size<T> and my own size() function. I tried to add ADL Barrier to size by looking at how it was used in other MPL components but it still fail to resolve the proper symbol under gcc 4.3. Any idea on what to do to fix that ?