diff --git a/services/core/java/com/android/server/connectivity/tethering/TetheringConfiguration.java b/services/core/java/com/android/server/connectivity/tethering/TetheringConfiguration.java
index d38beb3..44c61f0 100644
--- a/services/core/java/com/android/server/connectivity/tethering/TetheringConfiguration.java
+++ b/services/core/java/com/android/server/connectivity/tethering/TetheringConfiguration.java
@@ -16,6 +16,7 @@
 
 package com.android.server.connectivity.tethering;
 
+import static android.content.Context.TELEPHONY_SERVICE;
 import static android.net.ConnectivityManager.TYPE_MOBILE;
 import static android.net.ConnectivityManager.TYPE_MOBILE_DUN;
 import static android.net.ConnectivityManager.TYPE_MOBILE_HIPRI;
@@ -47,9 +48,9 @@
 public class TetheringConfiguration {
     private static final String TAG = TetheringConfiguration.class.getSimpleName();
 
-    private static final int DUN_NOT_REQUIRED = 0;
-    private static final int DUN_REQUIRED = 1;
-    private static final int DUN_UNSPECIFIED = 2;
+    public static final int DUN_NOT_REQUIRED = 0;
+    public static final int DUN_REQUIRED = 1;
+    public static final int DUN_UNSPECIFIED = 2;
 
     // USB is  192.168.42.1 and 255.255.255.0
     // Wifi is 192.168.43.1 and 255.255.255.0
@@ -81,8 +82,9 @@
         tetherableBluetoothRegexs = ctx.getResources().getStringArray(
                 com.android.internal.R.array.config_tether_bluetooth_regexs);
 
-        isDunRequired = checkDunRequired(ctx);
-        preferredUpstreamIfaceTypes = getUpstreamIfaceTypes(ctx, isDunRequired);
+        final int dunCheck = checkDunRequired(ctx);
+        preferredUpstreamIfaceTypes = getUpstreamIfaceTypes(ctx, dunCheck);
+        isDunRequired = preferredUpstreamIfaceTypes.contains(TYPE_MOBILE_DUN);
 
         dhcpRanges = getDhcpRanges(ctx);
         defaultIPv4DNS = copy(DEFAULT_IPV4_DNS);
@@ -138,14 +140,12 @@
         pw.println();
     }
 
-    private static boolean checkDunRequired(Context ctx) {
-        final TelephonyManager tm = ctx.getSystemService(TelephonyManager.class);
-        final int secureSetting =
-                (tm != null) ? tm.getTetherApnRequired() : DUN_UNSPECIFIED;
-        return (secureSetting == DUN_REQUIRED);
+    private static int checkDunRequired(Context ctx) {
+        final TelephonyManager tm = (TelephonyManager) ctx.getSystemService(TELEPHONY_SERVICE);
+        return (tm != null) ? tm.getTetherApnRequired() : DUN_UNSPECIFIED;
     }
 
-    private static Collection<Integer> getUpstreamIfaceTypes(Context ctx, boolean requiresDun) {
+    private static Collection<Integer> getUpstreamIfaceTypes(Context ctx, int dunCheck) {
         final int ifaceTypes[] = ctx.getResources().getIntArray(
                 com.android.internal.R.array.config_tether_upstream_types);
         final ArrayList<Integer> upstreamIfaceTypes = new ArrayList<>(ifaceTypes.length);
@@ -153,10 +153,10 @@
             switch (i) {
                 case TYPE_MOBILE:
                 case TYPE_MOBILE_HIPRI:
-                    if (requiresDun) continue;
+                    if (dunCheck == DUN_REQUIRED) continue;
                     break;
                 case TYPE_MOBILE_DUN:
-                    if (!requiresDun) continue;
+                    if (dunCheck == DUN_NOT_REQUIRED) continue;
                     break;
             }
             upstreamIfaceTypes.add(i);
@@ -166,7 +166,7 @@
         // of the value of |requiresDun|, cell data of one form or another is
         // *always* an upstream, regardless of the upstream interface types
         // specified by configuration resources.
-        if (requiresDun) {
+        if (dunCheck == DUN_REQUIRED) {
             if (!upstreamIfaceTypes.contains(TYPE_MOBILE_DUN)) {
                 upstreamIfaceTypes.add(TYPE_MOBILE_DUN);
             }
diff --git a/tests/net/java/com/android/server/connectivity/tethering/TetheringConfigurationTest.java b/tests/net/java/com/android/server/connectivity/tethering/TetheringConfigurationTest.java
new file mode 100644
index 0000000..9fcd1b5
--- /dev/null
+++ b/tests/net/java/com/android/server/connectivity/tethering/TetheringConfigurationTest.java
@@ -0,0 +1,132 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.server.connectivity.tethering;
+
+import static android.net.ConnectivityManager.TYPE_MOBILE;
+import static android.net.ConnectivityManager.TYPE_MOBILE_DUN;
+import static android.net.ConnectivityManager.TYPE_MOBILE_HIPRI;
+import static android.net.ConnectivityManager.TYPE_WIFI;
+import static com.android.server.connectivity.tethering.TetheringConfiguration.DUN_NOT_REQUIRED;
+import static com.android.server.connectivity.tethering.TetheringConfiguration.DUN_REQUIRED;
+import static com.android.server.connectivity.tethering.TetheringConfiguration.DUN_UNSPECIFIED;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+import static org.mockito.Mockito.when;
+
+import android.content.Context;
+import android.content.ContextWrapper;
+import android.content.res.Resources;
+import android.support.test.filters.SmallTest;
+import android.support.test.runner.AndroidJUnit4;
+import android.telephony.TelephonyManager;
+
+import com.android.internal.util.test.BroadcastInterceptingContext;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.Mock;
+import org.mockito.MockitoAnnotations;
+
+
+@RunWith(AndroidJUnit4.class)
+@SmallTest
+public class TetheringConfigurationTest {
+    @Mock private Context mContext;
+    @Mock private TelephonyManager mTelephonyManager;
+    @Mock private Resources mResources;
+    private Context mMockContext;
+    private boolean mHasTelephonyManager;
+
+    private class MockContext extends BroadcastInterceptingContext {
+        MockContext(Context base) {
+            super(base);
+        }
+
+        @Override
+        public Resources getResources() { return mResources; }
+
+        @Override
+        public Object getSystemService(String name) {
+            if (Context.TELEPHONY_SERVICE.equals(name)) {
+                return mHasTelephonyManager ? mTelephonyManager : null;
+            }
+            return super.getSystemService(name);
+        }
+    }
+
+    @Before
+    public void setUp() throws Exception {
+        MockitoAnnotations.initMocks(this);
+        when(mResources.getStringArray(com.android.internal.R.array.config_tether_dhcp_range))
+                .thenReturn(new String[0]);
+        when(mResources.getStringArray(com.android.internal.R.array.config_tether_usb_regexs))
+                .thenReturn(new String[0]);
+        when(mResources.getStringArray(com.android.internal.R.array.config_tether_wifi_regexs))
+                .thenReturn(new String[]{ "test_wlan\\d" });
+        when(mResources.getStringArray(com.android.internal.R.array.config_tether_bluetooth_regexs))
+                .thenReturn(new String[0]);
+        mMockContext = new MockContext(mContext);
+    }
+
+    @Test
+    public void testDunFromTelephonyManagerMeansDun() {
+        when(mResources.getIntArray(com.android.internal.R.array.config_tether_upstream_types))
+                .thenReturn(new int[]{TYPE_MOBILE, TYPE_WIFI, TYPE_MOBILE_HIPRI});
+        mHasTelephonyManager = true;
+        when(mTelephonyManager.getTetherApnRequired()).thenReturn(DUN_REQUIRED);
+
+        final TetheringConfiguration cfg = new TetheringConfiguration(mMockContext);
+        assertTrue(cfg.isDunRequired);
+        assertTrue(cfg.preferredUpstreamIfaceTypes.contains(TYPE_MOBILE_DUN));
+        assertFalse(cfg.preferredUpstreamIfaceTypes.contains(TYPE_MOBILE));
+        assertFalse(cfg.preferredUpstreamIfaceTypes.contains(TYPE_MOBILE_HIPRI));
+        // Just to prove we haven't clobbered Wi-Fi:
+        assertTrue(cfg.preferredUpstreamIfaceTypes.contains(TYPE_WIFI));
+    }
+
+    @Test
+    public void testDunNotRequiredFromTelephonyManagerMeansNoDun() {
+        when(mResources.getIntArray(com.android.internal.R.array.config_tether_upstream_types))
+                .thenReturn(new int[]{TYPE_MOBILE_DUN, TYPE_WIFI});
+        mHasTelephonyManager = true;
+        when(mTelephonyManager.getTetherApnRequired()).thenReturn(DUN_NOT_REQUIRED);
+
+        final TetheringConfiguration cfg = new TetheringConfiguration(mMockContext);
+        assertFalse(cfg.isDunRequired);
+        assertFalse(cfg.preferredUpstreamIfaceTypes.contains(TYPE_MOBILE_DUN));
+        assertTrue(cfg.preferredUpstreamIfaceTypes.contains(TYPE_MOBILE));
+        assertTrue(cfg.preferredUpstreamIfaceTypes.contains(TYPE_MOBILE_HIPRI));
+        // Just to prove we haven't clobbered Wi-Fi:
+        assertTrue(cfg.preferredUpstreamIfaceTypes.contains(TYPE_WIFI));
+    }
+
+    @Test
+    public void testDunFromUpstreamConfigMeansDun() {
+        when(mResources.getIntArray(com.android.internal.R.array.config_tether_upstream_types))
+                .thenReturn(new int[]{TYPE_MOBILE_DUN, TYPE_WIFI});
+        mHasTelephonyManager = false;
+        when(mTelephonyManager.getTetherApnRequired()).thenReturn(DUN_UNSPECIFIED);
+
+        final TetheringConfiguration cfg = new TetheringConfiguration(mMockContext);
+        assertTrue(cfg.isDunRequired);
+        assertTrue(cfg.preferredUpstreamIfaceTypes.contains(TYPE_MOBILE_DUN));
+        // Just to prove we haven't clobbered Wi-Fi:
+        assertTrue(cfg.preferredUpstreamIfaceTypes.contains(TYPE_WIFI));
+    }
+}