diff --git a/test/simple/test-cluster-disconnect-with-no-workers.js b/test/simple/test-cluster-disconnect-with-no-workers.js
index b05be777e6..48e3b09259 100644
--- a/test/simple/test-cluster-disconnect-with-no-workers.js
+++ b/test/simple/test-cluster-disconnect-with-no-workers.js
@@ -31,3 +31,6 @@ process.on('exit', function() {
 cluster.disconnect(function() {
   disconnected = true;
 });
+
+// Assert that callback is not sometimes synchronous
+assert(!disconnected);