diff --git a/framework/api/system-current.txt b/framework/api/system-current.txt
index 196e023..4a2ed8a 100644
--- a/framework/api/system-current.txt
+++ b/framework/api/system-current.txt
@@ -470,7 +470,7 @@
   }
 
   public abstract class SocketKeepalive implements java.lang.AutoCloseable {
-    method public final void start(@IntRange(from=0xa, to=0xe10) int, int, @NonNull android.net.Network);
+    method public final void start(@IntRange(from=0xa, to=0xe10) int, int, @Nullable android.net.Network);
     field public static final int ERROR_NO_SUCH_SLOT = -33; // 0xffffffdf
     field public static final int FLAG_AUTOMATIC_ON_OFF = 1; // 0x1
     field public static final int SUCCESS = 0; // 0x0
diff --git a/framework/src/android/net/SocketKeepalive.java b/framework/src/android/net/SocketKeepalive.java
index 311126e..10daf17 100644
--- a/framework/src/android/net/SocketKeepalive.java
+++ b/framework/src/android/net/SocketKeepalive.java
@@ -21,6 +21,7 @@
 import android.annotation.IntDef;
 import android.annotation.IntRange;
 import android.annotation.NonNull;
+import android.annotation.Nullable;
 import android.annotation.SystemApi;
 import android.os.Binder;
 import android.os.ParcelFileDescriptor;
@@ -374,12 +375,14 @@
      *                    the supplied {@link Callback} will see a call to
      *                    {@link Callback#onError(int)} with {@link #ERROR_INVALID_INTERVAL}.
      * @param flags Flags to enable/disable available options on this keepalive.
-     * @param underpinnedNetwork The underpinned network of this keepalive.
+     * @param underpinnedNetwork an optional network running over mNetwork that this
+     *                           keepalive is intended to keep up, e.g. an IPSec
+     *                           tunnel running over mNetwork.
      * @hide
      */
     @SystemApi(client = PRIVILEGED_APPS)
     public final void start(@IntRange(from = MIN_INTERVAL_SEC, to = MAX_INTERVAL_SEC)
-            int intervalSec, @StartFlags int flags, @NonNull Network underpinnedNetwork) {
+            int intervalSec, @StartFlags int flags, @Nullable Network underpinnedNetwork) {
         startImpl(intervalSec, flags, underpinnedNetwork);
     }
 
diff --git a/framework/src/android/net/TcpSocketKeepalive.java b/framework/src/android/net/TcpSocketKeepalive.java
index b548f6d..696889f 100644
--- a/framework/src/android/net/TcpSocketKeepalive.java
+++ b/framework/src/android/net/TcpSocketKeepalive.java
@@ -55,6 +55,12 @@
             throw new IllegalArgumentException("Illegal flag value for "
                     + this.getClass().getSimpleName() + " : " + flags);
         }
+
+        if (underpinnedNetwork != null) {
+            throw new IllegalArgumentException("Illegal underpinned network for "
+                    + this.getClass().getSimpleName() + " : " + underpinnedNetwork);
+        }
+
         mExecutor.execute(() -> {
             try {
                 mService.startTcpKeepalive(mNetwork, mPfd, intervalSec, mCallback);