diff --git a/README.md b/README.md
index 6b60bc7..65862b2 100644
--- a/README.md
+++ b/README.md
@@ -55,13 +55,18 @@ Here are some commands which can be sent to Kameleon Agent.
 #### cmd:list
 
 * `callback`: `<Function>`
+  * `err` : `<Error>`
   * `devices` : `<Array<DeviceObject>>`
 
 Request a list of available devices (ready to open -- _already plugged to USB or discovered wirelessly_) connected via serial ports.
 
 ```js
-socket_client.emit('cmd:list', (deviceObjects) => {
-  console.log(deviceObjects)
+socket_client.emit('cmd:list', (err, deviceObjects) => {
+  if (err) {
+    // handle error
+  } else {
+    console.log(deviceObjects)
+  }
 })
 ```
 
diff --git a/lib/session.js b/lib/session.js
index c0d71ab..cf7978e 100644
--- a/lib/session.js
+++ b/lib/session.js
@@ -160,16 +160,18 @@ class Session extends EventEmitter {
 
   /**
    * List all available devices
+   * @param {(err: Error, devices) => void} cb
    */
   list (cb) {
     SerialPort.list((err, portInfos) => {
       if (err) {
+        if (cb) cb(err);
         this.socket.emit('event:error', err)
       } else {
         this.portInfoArray = portInfos
           .filter(p => isSupported(p))
           .map(p => toDeviceObject(p))
-        if (cb) cb(this.portInfoArray)
+        if (cb) cb(null, this.portInfoArray)
         this.portInfoArray.forEach(p => {
           logger.info(`  [cmd:list] ${p.comName}`)
         })
diff --git a/package.json b/package.json
index 14ef5da..3b5e9fd 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "kameleon-agent",
-  "version": "0.8.0",
+  "version": "0.8.1",
   "author": "Minkyu Lee",
   "engines": {
     "node": "10.15.3"