diff --git a/services/device/serial/serial_io_handler_posix.cc b/services/device/serial/serial_io_handler_posix.cc
index 452d81538fd34..7f2a2c421b3f5 100644
--- a/services/device/serial/serial_io_handler_posix.cc
+++ b/services/device/serial/serial_io_handler_posix.cc
@@ -126,7 +126,11 @@ scoped_refptr<SerialIoHandler> SerialIoHandler::Create(
 void SerialIoHandlerPosix::ReadImpl() {
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
   DCHECK(pending_read_buffer());
-  DCHECK(file().IsValid());
+
+  if (!file().IsValid()) {
+    QueueReadCompleted(0, mojom::SerialReceiveError::DISCONNECTED);
+    return;
+  }
 
   // Try to read immediately. This is needed because on some platforms
   // (e.g., OSX) there may not be a notification from the message loop
@@ -138,7 +142,11 @@ void SerialIoHandlerPosix::ReadImpl() {
 void SerialIoHandlerPosix::WriteImpl() {
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
   DCHECK(pending_write_buffer());
-  DCHECK(file().IsValid());
+
+  if (!file().IsValid()) {
+    QueueWriteCompleted(0, mojom::SerialSendError::DISCONNECTED);
+    return;
+  }
 
   EnsureWatchingWrites();
 }
diff --git a/services/device/serial/serial_io_handler_win.cc b/services/device/serial/serial_io_handler_win.cc
index 29a69f2685df1..12d91e68ea9c5 100644
--- a/services/device/serial/serial_io_handler_win.cc
+++ b/services/device/serial/serial_io_handler_win.cc
@@ -266,7 +266,11 @@ bool SerialIoHandlerWin::PostOpen() {
 void SerialIoHandlerWin::ReadImpl() {
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
   DCHECK(pending_read_buffer());
-  DCHECK(file().IsValid());
+
+  if (!file().IsValid()) {
+    QueueReadCompleted(0, mojom::SerialReceiveError::DISCONNECTED);
+    return;
+  }
 
   if (!SetCommMask(file().GetPlatformFile(), EV_RXCHAR)) {
     VPLOG(1) << "Failed to set serial event flags";
@@ -285,7 +289,11 @@ void SerialIoHandlerWin::ReadImpl() {
 void SerialIoHandlerWin::WriteImpl() {
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
   DCHECK(pending_write_buffer());
-  DCHECK(file().IsValid());
+
+  if (!file().IsValid()) {
+    QueueWriteCompleted(0, mojom::SerialSendError::DISCONNECTED);
+    return;
+  }
 
   BOOL ok = ::WriteFile(file().GetPlatformFile(), pending_write_buffer(),
                         pending_write_buffer_len(), NULL,
diff --git a/services/device/serial/serial_port_impl_unittest.cc b/services/device/serial/serial_port_impl_unittest.cc
index 3618b88e916ec..93c7f0aa31714 100644
--- a/services/device/serial/serial_port_impl_unittest.cc
+++ b/services/device/serial/serial_port_impl_unittest.cc
@@ -21,9 +21,65 @@ class SerialPortImplTest : public DeviceServiceTestBase {
   ~SerialPortImplTest() override = default;
 
  protected:
+  void CreateDataPipe(mojo::ScopedDataPipeProducerHandle* producer,
+                      mojo::ScopedDataPipeConsumerHandle* consumer) {
+    MojoCreateDataPipeOptions options;
+    options.struct_size = sizeof(MojoCreateDataPipeOptions);
+    options.flags = MOJO_CREATE_DATA_PIPE_FLAG_NONE;
+    options.element_num_bytes = 1;
+    options.capacity_num_bytes = 64;
+
+    MojoResult result = mojo::CreateDataPipe(&options, producer, consumer);
+    DCHECK_EQ(result, MOJO_RESULT_OK);
+  }
+
+  mojo::ScopedDataPipeConsumerHandle StartReading(
+      mojom::SerialPort* serial_port) {
+    mojo::ScopedDataPipeProducerHandle producer;
+    mojo::ScopedDataPipeConsumerHandle consumer;
+    CreateDataPipe(&producer, &consumer);
+    serial_port->StartReading(std::move(producer));
+    return consumer;
+  }
+
+  mojo::ScopedDataPipeProducerHandle StartWriting(
+      mojom::SerialPort* serial_port) {
+    mojo::ScopedDataPipeProducerHandle producer;
+    mojo::ScopedDataPipeConsumerHandle consumer;
+    CreateDataPipe(&producer, &consumer);
+    serial_port->StartWriting(std::move(consumer));
+    return producer;
+  }
+
   DISALLOW_COPY_AND_ASSIGN(SerialPortImplTest);
 };
 
+TEST_F(SerialPortImplTest, StartIoBeforeOpen) {
+  mojo::Remote<mojom::SerialPort> serial_port;
+  mojo::PendingRemote<mojom::SerialPortConnectionWatcher> watcher_remote;
+  mojo::SelfOwnedReceiverRef<mojom::SerialPortConnectionWatcher> watcher =
+      mojo::MakeSelfOwnedReceiver(
+          std::make_unique<mojom::SerialPortConnectionWatcher>(),
+          watcher_remote.InitWithNewPipeAndPassReceiver());
+  SerialPortImpl::Create(
+      base::FilePath(FILE_PATH_LITERAL("/dev/fakeserialmojo")),
+      serial_port.BindNewPipeAndPassReceiver(), std::move(watcher_remote),
+      task_environment_.GetMainThreadTaskRunner());
+
+  mojo::ScopedDataPipeConsumerHandle consumer = StartReading(serial_port.get());
+  mojo::ScopedDataPipeProducerHandle producer = StartWriting(serial_port.get());
+
+  // Write some data so that StartWriting() will cause a call to Write().
+  static const char kBuffer[] = "test";
+  uint32_t bytes_written = base::size(kBuffer);
+  MojoResult result =
+      producer->WriteData(&kBuffer, &bytes_written, MOJO_WRITE_DATA_FLAG_NONE);
+  DCHECK_EQ(result, MOJO_RESULT_OK);
+  DCHECK_EQ(bytes_written, base::size(kBuffer));
+
+  base::RunLoop().RunUntilIdle();
+}
+
 TEST_F(SerialPortImplTest, WatcherClosedWhenPortClosed) {
   mojo::Remote<mojom::SerialPort> serial_port;
   mojo::PendingRemote<mojom::SerialPortConnectionWatcher> watcher;