diff --git a/lib/drivers/docker/container.js b/lib/drivers/docker/container.js
index <HASH>..<HASH> 100644
--- a/lib/drivers/docker/container.js
+++ b/lib/drivers/docker/container.js
@@ -214,7 +214,9 @@ Container.prototype.dockerEnv = function() {
 };
 
 Container.prototype.startArgs = function() {
-  var args = ['--cluster=0'];
+  var args = [
+    '--cluster=' + this.startOpts.size,
+  ];
   if (this.startOpts.trace) {
     args.push('--trace');
   }
docker: start cluster at full size