diff --git a/mobile/build.gradle.kts b/mobile/build.gradle.kts
index eede36a7..a8d5b21e 100644
--- a/mobile/build.gradle.kts
+++ b/mobile/build.gradle.kts
@@ -19,7 +19,7 @@ android {
         targetCompatibility(javaVersion)
     }
     kotlin.jvmToolchain(javaVersion)
-    compileSdk = 33
+    compileSdkPreview = "UpsideDownCake"
     defaultConfig {
         applicationId = "be.mygod.vpnhotspot"
         minSdk = 28
diff --git a/mobile/src/main/java/be/mygod/vpnhotspot/net/wifi/WifiApDialogFragment.kt b/mobile/src/main/java/be/mygod/vpnhotspot/net/wifi/WifiApDialogFragment.kt
index cbb249c9..61108ae0 100644
--- a/mobile/src/main/java/be/mygod/vpnhotspot/net/wifi/WifiApDialogFragment.kt
+++ b/mobile/src/main/java/be/mygod/vpnhotspot/net/wifi/WifiApDialogFragment.kt
@@ -22,6 +22,7 @@ import android.widget.Toast
 import androidx.annotation.RequiresApi
 import androidx.appcompat.app.AlertDialog
 import androidx.appcompat.widget.Toolbar
+import androidx.core.os.BuildCompat
 import androidx.core.os.persistableBundleOf
 import androidx.core.view.isGone
 import be.mygod.librootkotlinx.toByteArray
@@ -34,6 +35,7 @@ import be.mygod.vpnhotspot.databinding.DialogWifiApBinding
 import be.mygod.vpnhotspot.net.monitor.TetherTimeoutMonitor
 import be.mygod.vpnhotspot.util.QRCodeDialog
 import be.mygod.vpnhotspot.util.RangeInput
+import be.mygod.vpnhotspot.util.Services
 import be.mygod.vpnhotspot.util.readableMessage
 import be.mygod.vpnhotspot.util.showAllowingStateLoss
 import com.google.android.material.textfield.TextInputLayout
@@ -512,9 +514,14 @@ class WifiApDialogFragment : AlertDialogFragment<WifiApDialogFragment.Arg, WifiA
         val canCopy = timeoutError == null && bssidValid && maxClientError == null && listsNoError &&
                 bridgedTimeoutError == null && vendorElementsError == null && persistentRandomizedMacValid &&
                 acsNoError && bandwidthError == null
-        (dialog as? AlertDialog)?.getButton(DialogInterface.BUTTON_POSITIVE)?.isEnabled =
-            ssidOk && passwordValid && bandError == null && canCopy
-        dialogView.toolbar.menu.findItem(android.R.id.copy).isEnabled = canCopy
+        val canGenerate = ssidOk && passwordValid && bandError == null && canCopy
+        (dialog as? AlertDialog)?.getButton(DialogInterface.BUTTON_POSITIVE)?.isEnabled = canGenerate
+        dialogView.toolbar.menu.apply {
+            findItem(R.id.invalid).isVisible = canGenerate && !arg.p2pMode && !arg.readOnly &&
+                    BuildCompat.isAtLeastU() &&
+                    !Services.wifi.validateSoftApConfiguration(generateConfig().toPlatform())
+            findItem(android.R.id.copy).isEnabled = canCopy
+        }
     }
 
     override fun onTextChanged(s: CharSequence, start: Int, before: Int, count: Int) { }
diff --git a/mobile/src/main/res/menu/toolbar_configuration.xml b/mobile/src/main/res/menu/toolbar_configuration.xml
index c7448942..6e48873f 100644
--- a/mobile/src/main/res/menu/toolbar_configuration.xml
+++ b/mobile/src/main/res/menu/toolbar_configuration.xml
@@ -1,6 +1,14 @@
 <?xml version="1.0" encoding="utf-8"?>
 <menu xmlns:android="http://schemas.android.com/apk/res/android"
-      xmlns:app="http://schemas.android.com/apk/res-auto">
+      xmlns:app="http://schemas.android.com/apk/res-auto"
+      xmlns:tools="http://schemas.android.com/tools">
+    <item android:id="@+id/invalid"
+        android:icon="@drawable/ic_alert_warning"
+        android:visible="false"
+        android:title="@string/configuration_invalid"
+        app:iconTint="@color/design_default_color_error"
+        app:showAsAction="always"
+        tools:visible="true"/>
     <item android:id="@android:id/copy"
           android:alphabeticShortcut="c"
           android:icon="?attr/actionModeCopyDrawable"
diff --git a/mobile/src/main/res/values-zh-rCN/strings.xml b/mobile/src/main/res/values-zh-rCN/strings.xml
index 5036e867..7f1dbb57 100644
--- a/mobile/src/main/res/values-zh-rCN/strings.xml
+++ b/mobile/src/main/res/values-zh-rCN/strings.xml
@@ -174,6 +174,7 @@
     <string name="permission_missing">权限不足</string>
 
     <string name="configuration_view">设置 WLAN</string>
+    <string name="configuration_invalid">配置可能无效</string>
     <string name="configuration_share">使用 QR 码分享</string>
     <string name="configuration_rejected">Android 系统拒绝使用此配置。（详情参见日志）</string>
     <string name="wifi_ssid" msgid="5519636102673067319">"网络名称"</string>
diff --git a/mobile/src/main/res/values/strings.xml b/mobile/src/main/res/values/strings.xml
index 842561b4..57c41905 100644
--- a/mobile/src/main/res/values/strings.xml
+++ b/mobile/src/main/res/values/strings.xml
@@ -199,6 +199,7 @@
     <string name="permission_missing">Permission missing</string>
 
     <string name="configuration_view">Wi\u2011Fi configuration</string>
+    <string name="configuration_invalid">Possibly invalid configuration</string>
     <string name="configuration_share">Share via QR code</string>
     <string name="configuration_rejected">Android system refuses such configuration. (see logcat)</string>
     <string name="wifi_ssid">Network name</string>