diff --git a/server/core/dcb.cc b/server/core/dcb.cc
index a75184fe6..c9af9a270 100644
--- a/server/core/dcb.cc
+++ b/server/core/dcb.cc
@@ -1006,6 +1006,8 @@ static void dcb_log_write_failure(DCB* dcb, GWBUF* queue, int eno)
  */
 int dcb_drain_writeq(DCB* dcb)
 {
+    mxb_assert(dcb->poll.owner == RoutingWorker::get_current());
+
     if (dcb->ssl_read_want_write)
     {
         /** The SSL library needs to write more data */