diff --git a/lib/cluster.js b/lib/cluster.js
index 50a94f1d0f1..72060c4dd2b 100644
--- a/lib/cluster.js
+++ b/lib/cluster.js
@@ -264,6 +264,7 @@ function masterInit() {
 
     process.on('internalMessage', function(message) {
       if (message.cmd !== 'NODE_DEBUG_ENABLED') return;
+      var key;
       for (key in cluster.workers)
         process._debugProcess(cluster.workers[key].process.pid);
     });