Is this an rvalue reference problem?

[Gary Willoughby via Digitalmars-d-learn]

See the following code:

import std.stdio;
void foo(ref int x)
{
        writefln("%s", x);
}

void main(string[] args)
{
        int y = 0;
        foo(y++);
}

When compiled it produces this error:

test.d(11): Error: function test.foo (ref int x) is not callable 
using argument types (int)

If I remove the post-increment of the y variable if works. Is 
this an rvalue reference issue? Would you expect this to work? 
Should the error message be a little more helpful?