diff --git a/android/app/src/main/java/com/eddy/atomrelay/EspFlasher.kt b/android/app/src/main/java/com/eddy/atomrelay/EspFlasher.kt
index 03e3eef..480c410 100644
--- a/android/app/src/main/java/com/eddy/atomrelay/EspFlasher.kt
+++ b/android/app/src/main/java/com/eddy/atomrelay/EspFlasher.kt
@@ -25,7 +25,15 @@ class EspFlasher(private val context: Context) {
 
     private val handler = Handler(Looper.getMainLooper())
 
+    @Volatile
+    private var cancelled = false
+
+    fun cancel() {
+        cancelled = true
+    }
+
     fun flashDevice(usbManager: UsbManager, device: UsbDevice, callback: FlashCallback) {
+        cancelled = false
         Thread {
             try {
                 doFlash(usbManager, device, callback)
@@ -47,6 +55,7 @@ class EspFlasher(private val context: Context) {
 
     private fun doFlash(usbManager: UsbManager, device: UsbDevice, callback: FlashCallback) {
         Thread.sleep(500)
+        if (cancelled) return
 
         val connection = usbManager.openDevice(device)
             ?: throw IOException("Kan USB-apparaat niet openen")
@@ -67,6 +76,7 @@ class EspFlasher(private val context: Context) {
             postProgress(callback, 0, "Verbinden met ESP bootloader...")
 
             val transport = UsbSerialTransport(connection, epOut, epIn)
+            if (cancelled) return
 
             val assets = context.assets
             val bootloader = assets.open("firmware/bootloader.bin").readBytes()
@@ -107,6 +117,7 @@ class EspFlasher(private val context: Context) {
             stub.eraseFlash()
 
             for (step in steps) {
+                if (cancelled) return
                 val sizeStr = if (step.data.size > 1024) "${step.data.size / 1024}KB" else "${step.data.size} bytes"
                 postProgress(callback, step.baseProgress, "${step.name} schrijven ($sizeStr)...")
 
diff --git a/android/app/src/main/java/com/eddy/atomrelay/SettingsActivity.kt b/android/app/src/main/java/com/eddy/atomrelay/SettingsActivity.kt
index ccfecb3..3b6563b 100644
--- a/android/app/src/main/java/com/eddy/atomrelay/SettingsActivity.kt
+++ b/android/app/src/main/java/com/eddy/atomrelay/SettingsActivity.kt
@@ -43,6 +43,7 @@ class SettingsActivity : AppCompatActivity() {
     private var currentAction = UsbAction.NONE
     private var progressDialog: AlertDialog? = null
     private var dialog: AlertDialog? = null
+    private var flasher: EspFlasher? = null
     private val handler = Handler(Looper.getMainLooper())
 
     private val usbAttachedReceiver = object : BroadcastReceiver() {
@@ -120,6 +121,8 @@ class SettingsActivity : AppCompatActivity() {
     override fun onDestroy() {
         super.onDestroy()
         currentAction = UsbAction.NONE
+        flasher?.cancel()
+        flasher = null
         try { unregisterReceiver(usbAttachedReceiver) } catch (e: Exception) {}
         try { unregisterReceiver(usbPermissionReceiver) } catch (e: Exception) {}
         try { unregisterReceiver(usbDetachedReceiver) } catch (e: Exception) {}
@@ -203,8 +206,8 @@ class SettingsActivity : AppCompatActivity() {
     private fun doFlashing(usbManager: UsbManager, device: UsbDevice) {
         showProgressDialog("Firmware Flashen", "Initialiseren...", STYLE_HORIZONTAL)
 
-        val flasher = EspFlasher(this)
-        flasher.flashDevice(usbManager, device, object : EspFlasher.FlashCallback {
+        flasher = EspFlasher(this)
+        flasher?.flashDevice(usbManager, device, object : EspFlasher.FlashCallback {
             override fun onProgress(percent: Int, message: String) {
                 runOnUiThread {
                     val d = progressDialog ?: return@runOnUiThread