diff --git a/doc/dev/loopmgr.md b/doc/dev/loopmgr.md
index 9c4518154c..15831e6236 100644
--- a/doc/dev/loopmgr.md
+++ b/doc/dev/loopmgr.md
@@ -104,3 +104,13 @@ functions MUST be called from the thread that created the network manager
 socket.
 
 The ``isc_nm_listen*()`` functions MUST be called from the ``main`` loop.
+
+The general design of Network Manager is based on callbacks.  An extra care must
+be taken when implementing new functions because the callbacks MUST be called
+asynchronously because the caller might be inside a lock and the same lock must
+be acquired in the callback.  This doesn't mean that the callback must be always
+called asynchronously, because sometimes we are already in the libuv callback
+and thus we can just call the callback directly, but in other places, especially
+when returning an error, the control hasn't been returned to the caller yet and
+in such case, the callback must be scheduled onto the event loop instead of
+executing it directly.
diff --git a/lib/isc/netmgr/udp.c b/lib/isc/netmgr/udp.c
index 9b715d9b6c..587e368203 100644
--- a/lib/isc/netmgr/udp.c
+++ b/lib/isc/netmgr/udp.c
@@ -685,6 +685,7 @@ isc__nm_udp_send(isc_nmhandle_t *handle, const isc_region_t *region,
 	isc__networker_t *worker = NULL;
 	uint32_t maxudp;
 	int r;
+	isc_result_t result;
 
 	REQUIRE(VALID_NMSOCK(sock));
 	REQUIRE(sock->type == isc_nm_udpsocket);
@@ -706,16 +707,6 @@ isc__nm_udp_send(isc_nmhandle_t *handle, const isc_region_t *region,
 		return;
 	}
 
-	if (isc__nm_closing(worker)) {
-		cb(handle, ISC_R_SHUTTINGDOWN, cbarg);
-		return;
-	}
-
-	if (isc__nmsocket_closing(sock)) {
-		cb(handle, ISC_R_CANCELED, cbarg);
-		return;
-	}
-
 	uvreq = isc__nm_uvreq_get(sock->worker, sock);
 	uvreq->uvbuf.base = (char *)region->base;
 	uvreq->uvbuf.len = region->length;
@@ -725,6 +716,16 @@ isc__nm_udp_send(isc_nmhandle_t *handle, const isc_region_t *region,
 	uvreq->cb.send = cb;
 	uvreq->cbarg = cbarg;
 
+	if (isc__nm_closing(worker)) {
+		result = ISC_R_SHUTTINGDOWN;
+		goto fail;
+	}
+
+	if (isc__nmsocket_closing(sock)) {
+		result = ISC_R_CANCELED;
+		goto fail;
+	}
+
 	/*
 	 * We used uv_udp_connect(), so the peer address has to be
 	 * set to NULL or else uv_udp_send() could fail or assert,
@@ -738,8 +739,12 @@ isc__nm_udp_send(isc_nmhandle_t *handle, const isc_region_t *region,
 			&uvreq->uvbuf, 1, sa, udp_send_cb);
 	if (r < 0) {
 		isc__nm_incstats(sock, STATID_SENDFAIL);
-		isc__nm_failed_send_cb(sock, uvreq, isc_uverr2result(r));
+		result = isc_uverr2result(r);
+		goto fail;
 	}
+	return;
+fail:
+	isc__nm_failed_send_cb(sock, uvreq, result);
 }
 
 static isc_result_t