diff --git a/examplemultipleports/src/main/java/com/felhr/examplemultipleports/UsbService.java b/examplemultipleports/src/main/java/com/felhr/examplemultipleports/UsbService.java
index 4f5d04d..dae18a6 100644
--- a/examplemultipleports/src/main/java/com/felhr/examplemultipleports/UsbService.java
+++ b/examplemultipleports/src/main/java/com/felhr/examplemultipleports/UsbService.java
@@ -157,6 +157,8 @@ public class UsbService extends Service implements SerialPortCallback {
     @Override
     public void onDestroy() {
         super.onDestroy();
+        if(builder != null)
+            builder.unregisterListeners(context);
         UsbService.SERVICE_CONNECTED = false;
     }
 
@@ -232,8 +234,10 @@ public class UsbService extends Service implements SerialPortCallback {
                 public void handleMessage(Message msg) {
                     int port = msg.arg1;
                     byte[] data = (byte[]) msg.obj;
-                    UsbSerialDevice serialDevice = serialPorts.get(port);
-                    serialDevice.getOutputStream().write(data);
+                    if(port <= serialPorts.size()-1) {
+                        UsbSerialDevice serialDevice = serialPorts.get(port);
+                        serialDevice.getOutputStream().write(data);
+                    }
                 }
             };
             Looper.loop();
diff --git a/usbserial/src/main/java/com/felhr/usbserial/SerialPortBuilder.java b/usbserial/src/main/java/com/felhr/usbserial/SerialPortBuilder.java
index ef5b503..923cdf7 100644
--- a/usbserial/src/main/java/com/felhr/usbserial/SerialPortBuilder.java
+++ b/usbserial/src/main/java/com/felhr/usbserial/SerialPortBuilder.java
@@ -146,6 +146,13 @@ public class SerialPortBuilder {
         return false;
     }
 
+    public void unregisterListeners(Context context){
+        if(broadcastRegistered){
+            context.unregisterReceiver(usbReceiver);
+            broadcastRegistered = false;
+        }
+    }
+
     private PendingUsbPermission createUsbPermission(Context context, UsbDeviceStatus usbDeviceStatus){
         PendingIntent mPendingIntent = PendingIntent.getBroadcast(context, 0, new Intent(ACTION_USB_PERMISSION), 0);
         PendingUsbPermission pendingUsbPermission = new PendingUsbPermission();