Thanks. That works.

But then the docs are misleading. Quote from perldoc Thread::Queue::Any:

dequeue
($string,$scalar,$listref,$hashref) = $queue->dequeue;

The "dequeue" method removes a reference from the head of the queue, dereferences it and returns the resulting values. If the queue is currently empty, "dequeue" will block the thread until another thread "enqueue"s.

If I enqueue() a scalar I expect to dequeue() a scalar and not a list.