diff --git a/src/messages.jl b/src/messages.jl
index bbfb13f..f8e1da1 100644
--- a/src/messages.jl
+++ b/src/messages.jl
@@ -147,6 +147,7 @@ function flush_gc_msgs(w::Worker)
     end
 
     # del_msgs gets populated by finalizers, so be very careful here about ordering of allocations
+    # XXX: threading requires this to be atomic
     new_array = Any[]
     msgs = w.del_msgs
     w.del_msgs = new_array
@@ -178,7 +179,7 @@ function send_msg_(w::Worker, header, msg, now::Bool)
         wait(w.initialized)
     end
     io = w.w_stream
-    lock(io.lock)
+    lock(io)
     try
         reset_state(w.w_serializer)
         serialize_hdr_raw(io, header)
@@ -191,7 +192,7 @@ function send_msg_(w::Worker, header, msg, now::Bool)
             flush(io)
         end
     finally
-        unlock(io.lock)
+        unlock(io)
     end
 end