diff --git a/lib/monitor.js b/lib/monitor.js
index a15bc2e..a97dfae 100644
--- a/lib/monitor.js
+++ b/lib/monitor.js
@@ -296,7 +296,9 @@ Monitor.prototype._connectProcSock = function (socket) {
 
     if (Array.isArray(socks) && socks.length > 0) {
       socks.forEach(function (sock) {
-        canNotBeDeleted[sock.pid.toString()] = 1;
+        if (sock._pid) {
+          canNotBeDeleted[sock._pid.toString()] = 1;
+        }
       });
     }