m_condition.mutex cannot be used in shared method ?

[Marco Leise via Digitalmars-d-learn]

I have a thread that is shared by
others, so I have a shared method, inside of which I wrote:

final void opOpAssign(string op : "~")(ref StreamingObject item) shared
{
        synchronized (m_condition.mutex)
        {
                m_list.unshared ~= item;
                m_condition.notify();
        }
}

Error: non-shared method core.sync.condition.Condition.mutex is not callable 
using a shared object

Where exactly should my stuff stop to be shared so I can call .mutex ?

Btw.:
StreamingObject is a struct
unshared is a @property that casts away sharedness

-- 
Marco