diff --git a/src/CommandBusClient.php b/src/CommandBusClient.php
index c8d3c98..880f8de 100644
--- a/src/CommandBusClient.php
+++ b/src/CommandBusClient.php
@@ -143,8 +143,8 @@ class CommandBusClient implements CommandBusInterface
     public function execute(string $command, array $context): PromiseInterface
     {
         if (!$this->connection) {
-            return new Promise(function (callable $resolve) {
-                $resolve(new \RuntimeException("Not connected to command bus."));
+            return new Promise(function (callable $resolve, callable $canceller) {
+                $canceller("Not connected to command bus.");
             });
         }