diff --git a/nodes/core/io/10-mqtt.js b/nodes/core/io/10-mqtt.js
index 4e65bd39b..9085505c7 100644
--- a/nodes/core/io/10-mqtt.js
+++ b/nodes/core/io/10-mqtt.js
@@ -45,21 +45,26 @@ module.exports = function(RED) {
             this.status({fill:"red",shape:"ring",text:"disconnected"});
             this.client = connectionPool.get(this.brokerConfig.broker,this.brokerConfig.port,this.brokerConfig.clientid,this.brokerConfig.username,this.brokerConfig.password);
             var node = this;
-            this.client.subscribe(this.topic,2,function(topic,payload,qos,retain) {
-                if (isUtf8(payload)) { payload = payload.toString(); }
-                var msg = {topic:topic,payload:payload,qos:qos,retain:retain};
-                if ((node.brokerConfig.broker === "localhost")||(node.brokerConfig.broker === "127.0.0.1")) {
-                    msg._topic = topic;
-                }
-                node.send(msg);
-            });
-            this.client.on("connectionlost",function() {
-                node.status({fill:"red",shape:"ring",text:"disconnected"});
-            });
-            this.client.on("connect",function() {
-                node.status({fill:"green",shape:"dot",text:"connected"});
-            });
-            this.client.connect();
+            if (this.topic) {
+                this.client.subscribe(this.topic,2,function(topic,payload,qos,retain) {
+                    if (isUtf8(payload)) { payload = payload.toString(); }
+                    var msg = {topic:topic,payload:payload,qos:qos,retain:retain};
+                    if ((node.brokerConfig.broker === "localhost")||(node.brokerConfig.broker === "127.0.0.1")) {
+                        msg._topic = topic;
+                    }
+                    node.send(msg);
+                });
+                this.client.on("connectionlost",function() {
+                    node.status({fill:"red",shape:"ring",text:"disconnected"});
+                });
+                this.client.on("connect",function() {
+                    node.status({fill:"green",shape:"dot",text:"connected"});
+                });
+                this.client.connect();
+            }
+            else {
+                this.error("topic not defined");
+            }
         } else {
             this.error("missing broker configuration");
         }