lib\pure\asyncmacro.nim(43, 27) Error: attempting to call undeclared routine: 'callback='

[monster]

Hi,

I've just finished coding some async "cluster networking" prototype (using 
asyncnet), and I'm getting a compiler error that I don't undertand (don't know 
how to fix), while writing my first test module for it:
    
    
    import asyncdispatch
    import asyncnet
    
    # ...
    
    type
      QueueID* = distinct uint32
      Msg*[T: not (ref|string|seq)] = object
        # ...
    
    # ...
    
    # Forward declaration:
    proc sendMsgExternally[T](q: QueueID, m: ptr[Msg[T]], size: uint32) 
{.async.}
    
    proc fillAndSendMsg[T](q: QueueID, m: ptr[Msg[T]], buffered: bool): void =
      # ...
      let size = uint32(sizeof(Msg[T]))
      asyncCheck sendMsgExternally(q, m, size)
    

and on that last line, I am getting this error:
    
    
    lib\pure\asyncmacro.nim(43, 27) Error: attempting to call undeclared 
routine: 'callback='
    

The content of sendMsgExternally() makes no difference; I replaced it with 
"discard", and the error stays. This is the only error I'm getting, so it's not 
a consequence of a previous error. Google was no help for this one.