diff --git a/core/java/android/net/TcpSocketKeepalive.java b/core/java/android/net/TcpSocketKeepalive.java
index 8f6ee7b..f691a0d 100644
--- a/core/java/android/net/TcpSocketKeepalive.java
+++ b/core/java/android/net/TcpSocketKeepalive.java
@@ -45,13 +45,14 @@
      * - The application must not write to or read from the socket after calling this method, until
      *   onDataReceived, onStopped, or onError are called. If it does, the keepalive will fail
      *   with {@link #ERROR_SOCKET_NOT_IDLE}, or {@code #ERROR_INVALID_SOCKET} if the socket
-     *   experienced an error (as in poll(2) returned POLLERR); if this happens, the data received
-     *   from the socket may be invalid, and the socket can't be recovered.
+     *   experienced an error (as in poll(2) returned POLLERR or POLLHUP); if this happens, the data
+     *   received from the socket may be invalid, and the socket can't be recovered.
      * - If the socket has data in the send or receive buffer, then this call will fail with
      *   {@link #ERROR_SOCKET_NOT_IDLE} and can be retried after the data has been processed.
-     *   An app could ensure this by using an application-layer protocol where it can receive
-     *   acknowledgement that it will go into keepalive mode. It could then go into keepalive
-     *   mode after having read the acknowledgement, draining the socket.
+     *   An app could ensure this by using an application-layer protocol to receive acknowledgement
+     *   that indicates all data has been delivered to server, e.g. HTTP 200 OK.
+     *   Then the app could go into keepalive mode after reading all remaining data within the
+     *   acknowledgement.
      */
     @Override
     void startImpl(int intervalSec) {
diff --git a/services/core/java/com/android/server/connectivity/KeepaliveTracker.java b/services/core/java/com/android/server/connectivity/KeepaliveTracker.java
index 6cff57d..cc4c173 100644
--- a/services/core/java/com/android/server/connectivity/KeepaliveTracker.java
+++ b/services/core/java/com/android/server/connectivity/KeepaliveTracker.java
@@ -239,7 +239,12 @@
                                 .sendMessage(CMD_START_SOCKET_KEEPALIVE, slot, mInterval, mPacket);
                         break;
                     case TYPE_TCP:
-                        mTcpController.startSocketMonitor(mFd, this, mSlot);
+                        try {
+                            mTcpController.startSocketMonitor(mFd, this, mSlot);
+                        } catch (InvalidSocketException e) {
+                            handleStopKeepalive(mNai, mSlot, ERROR_INVALID_SOCKET);
+                            return;
+                        }
                         mNai.asyncChannel
                                 .sendMessage(CMD_ADD_KEEPALIVE_PACKET_FILTER, slot, 0 /* Unused */,
                                         mPacket);
diff --git a/services/core/java/com/android/server/connectivity/TcpKeepaliveController.java b/services/core/java/com/android/server/connectivity/TcpKeepaliveController.java
index 65de83b..3e21b5b 100644
--- a/services/core/java/com/android/server/connectivity/TcpKeepaliveController.java
+++ b/services/core/java/com/android/server/connectivity/TcpKeepaliveController.java
@@ -215,18 +215,20 @@
      * Start monitoring incoming packets.
      *
      * @param fd socket fd to monitor.
-     * @param messenger a callback to notify socket status.
+     * @param ki a {@link KeepaliveInfo} that tracks information about a socket keepalive.
      * @param slot keepalive slot.
      */
     public void startSocketMonitor(@NonNull final FileDescriptor fd,
-            @NonNull final KeepaliveInfo ki, final int slot) {
+            @NonNull final KeepaliveInfo ki, final int slot)
+            throws IllegalArgumentException, InvalidSocketException {
         synchronized (mListeners) {
             if (null != mListeners.get(slot)) {
                 throw new IllegalArgumentException("This slot is already taken");
             }
             for (int i = 0; i < mListeners.size(); ++i) {
                 if (fd.equals(mListeners.valueAt(i))) {
-                    throw new IllegalArgumentException("This fd is already registered");
+                    Log.e(TAG, "This fd is already registered.");
+                    throw new InvalidSocketException(ERROR_INVALID_SOCKET);
                 }
             }
             mFdHandlerQueue.addOnFileDescriptorEventListener(fd, FD_EVENTS, (readyFd, events) -> {