diff --git a/app/src/main/java/com/wireguard/android/fragment/TunnelController.java b/app/src/main/java/com/wireguard/android/fragment/TunnelController.java
new file mode 100644
index 00000000..668e74c0
--- /dev/null
+++ b/app/src/main/java/com/wireguard/android/fragment/TunnelController.java
@@ -0,0 +1,71 @@
+package com.wireguard.android.fragment;
+
+import android.app.AlertDialog;
+import android.content.Context;
+import android.databinding.DataBindingUtil;
+import android.databinding.ViewDataBinding;
+import android.system.ErrnoException;
+import android.system.OsConstants;
+import android.text.Html;
+import android.text.method.LinkMovementMethod;
+import android.util.Log;
+import android.view.View;
+import android.widget.TextView;
+
+import com.commonsware.cwac.crossport.design.widget.Snackbar;
+import com.wireguard.android.R;
+import com.wireguard.android.databinding.TunnelDetailFragmentBinding;
+import com.wireguard.android.databinding.TunnelListItemBinding;
+import com.wireguard.android.model.Tunnel;
+import com.wireguard.android.model.Tunnel.State;
+import com.wireguard.android.util.ExceptionLoggers;
+
+/**
+ * Helper method shared by TunnelListFragment and TunnelDetailFragment.
+ */
+
+public final class TunnelController {
+    private static final String TAG = TunnelController.class.getSimpleName();
+
+    private TunnelController() {
+        // Prevent instantiation.
+    }
+
+    public static void setTunnelState(final View view, final boolean checked) {
+        final ViewDataBinding binding = DataBindingUtil.findBinding(view);
+        final Tunnel tunnel;
+        if (binding instanceof TunnelDetailFragmentBinding)
+            tunnel = ((TunnelDetailFragmentBinding) binding).getTunnel();
+        else if (binding instanceof TunnelListItemBinding)
+            tunnel = ((TunnelListItemBinding) binding).getItem();
+        else
+            tunnel = null;
+        if (tunnel == null) {
+            Log.e(TAG, "setChecked() from a null tunnel", new IllegalStateException());
+            return;
+        }
+        tunnel.setState(State.of(checked)).whenComplete((state, throwable) -> {
+            if (throwable == null)
+                return;
+            Log.e(TAG, "Cannot set state of tunnel " + tunnel.getName(), throwable);
+            final Context context = view.getContext();
+            if (throwable instanceof ErrnoException
+                    && ((ErrnoException) throwable).errno == OsConstants.ENODEV) {
+                final String message = context.getString(R.string.not_supported_message);
+                final AlertDialog dialog = new AlertDialog.Builder(context)
+                        .setMessage(Html.fromHtml(message))
+                        .setPositiveButton(R.string.ok, null)
+                        .setTitle(R.string.not_supported_title)
+                        .show();
+                // Make links work.
+                ((TextView) dialog.findViewById(android.R.id.message))
+                        .setMovementMethod(LinkMovementMethod.getInstance());
+            } else {
+                final String message =
+                        context.getString(checked ? R.string.error_up : R.string.error_down) + ": "
+                                + ExceptionLoggers.unwrap(throwable).getMessage();
+                Snackbar.make(view, message, Snackbar.LENGTH_LONG).show();
+            }
+        });
+    }
+}
diff --git a/app/src/main/res/layout/tunnel_detail_fragment.xml b/app/src/main/res/layout/tunnel_detail_fragment.xml
index e10bc4e1..900d08ed 100644
--- a/app/src/main/res/layout/tunnel_detail_fragment.xml
+++ b/app/src/main/res/layout/tunnel_detail_fragment.xml
@@ -5,6 +5,8 @@
 
     <data>
 
+        <import type="com.wireguard.android.fragment.TunnelController" />
+
         <import type="com.wireguard.android.model.Tunnel.State" />
 
         <import type="com.wireguard.android.util.ClipboardUtils" />
@@ -52,7 +54,7 @@
                     android:layout_alignBaseline="@+id/interface_title"
                     android:layout_alignParentEnd="true"
                     app:checked="@{tunnel.state == State.UP}"
-                    app:onBeforeCheckedChanged="@{() -> tunnel.setState(State.TOGGLE)}" />
+                    app:onBeforeCheckedChanged="@{TunnelController::setTunnelState}" />
 
                 <TextView
                     android:id="@+id/interface_name_label"
diff --git a/app/src/main/res/layout/tunnel_list_item.xml b/app/src/main/res/layout/tunnel_list_item.xml
index 1ed157e9..7fbd61f7 100644
--- a/app/src/main/res/layout/tunnel_list_item.xml
+++ b/app/src/main/res/layout/tunnel_list_item.xml
@@ -4,6 +4,8 @@
 
     <data>
 
+        <import type="com.wireguard.android.fragment.TunnelController" />
+
         <import type="com.wireguard.android.model.Tunnel" />
 
         <import type="com.wireguard.android.model.Tunnel.State" />
@@ -47,6 +49,6 @@
             android:layout_alignBaseline="@+id/tunnel_name"
             android:layout_alignParentEnd="true"
             app:checked="@{item.state == State.UP}"
-            app:onBeforeCheckedChanged="@{() -> item.setState(State.TOGGLE)}" />
+            app:onBeforeCheckedChanged="@{TunnelController::setTunnelState}" />
     </RelativeLayout>
 </layout>
diff --git a/app/src/main/res/values/strings.xml b/app/src/main/res/values/strings.xml
index f32a9925..f7b4c548 100644
--- a/app/src/main/res/values/strings.xml
+++ b/app/src/main/res/values/strings.xml
@@ -16,7 +16,6 @@
     <string name="edit">Edit</string>
     <string name="endpoint">Endpoint</string>
     <string name="error_down">Error bringing down WireGuard tunnel</string>
-    <string name="error_su">WireGuard currently requires root access</string>
     <string name="error_up">Error bringing up WireGuard tunnel</string>
     <string name="generate">Generate</string>
     <string name="hint_automatic">(auto)</string>