diff --git a/libovccclient/src/ovccclient-server.vala b/libovccclient/src/ovccclient-server.vala
index 209c401d3de6a1d95fd2c1635c35d366e50e3ec6..3048730f5b1ec360ac66e33fdb3b165027c4d048 100644
--- a/libovccclient/src/ovccclient-server.vala
+++ b/libovccclient/src/ovccclient-server.vala
@@ -277,6 +277,8 @@ namespace OVCCClient
     {
       if (AtomicInt.get (ref send_loop_running) == 0) {
         throw new ServerError.COMMUNICATION_FAILED ("Send loop is not running");
+      } else if (msg == null) { /* send_loop_queue.push needs non-null */
+        throw new ServerError.COMMUNICATION_FAILED ("Message to send is null");
       } else {
         ulong         id = 0;
         ulong         cancel_id = 0;