diff --git a/web_transport/sdk/impl/web_transport_stream_impl.cc b/web_transport/sdk/impl/web_transport_stream_impl.cc
index 8117a45..83c7208 100644
--- a/web_transport/sdk/impl/web_transport_stream_impl.cc
+++ b/web_transport/sdk/impl/web_transport_stream_impl.cc
@@ -120,22 +120,85 @@ size_t WebTransportStreamImpl::Read(uint8_t* data, size_t length) {
 }
 
 size_t WebTransportStreamImpl::ReadableBytes() const {
-  return stream_->ReadableBytes();
+  if (io_runner_->BelongsToCurrentThread()) {
+    return stream_->ReadableBytes();
+  }
+  size_t result;
+  base::WaitableEvent done(base::WaitableEvent::ResetPolicy::AUTOMATIC,
+                           base::WaitableEvent::InitialState::NOT_SIGNALED);
+  io_runner_->PostTask(
+      FROM_HERE,
+      base::BindOnce(
+          [](WebTransportStreamImpl const* stream, size_t& result,
+             base::WaitableEvent* event) {
+            result = stream->stream_->ReadableBytes();
+            event->Signal();
+          },
+          base::Unretained(this), std::ref(result), base::Unretained(&done)));
+  done.Wait();
+  return result;
 }
 
 void WebTransportStreamImpl::Close() {
-  // TODO: Post to IO runner.
-  if (!stream_->SendFin()) {
-    LOG(ERROR) << "Failed to send FIN.";
+  if (io_runner_->BelongsToCurrentThread()) {
+    if (!stream_->SendFin()) {
+      LOG(ERROR) << "Failed to send FIN.";
+    }
+    return;
   }
+  base::WaitableEvent done(base::WaitableEvent::ResetPolicy::AUTOMATIC,
+                           base::WaitableEvent::InitialState::NOT_SIGNALED);
+  io_runner_->PostTask(
+      FROM_HERE,
+      base::BindOnce(
+          [](WebTransportStreamImpl* stream, base::WaitableEvent* event) {
+            if (!stream->stream_->SendFin()) {
+              LOG(ERROR) << "Failed to send FIN.";
+            }
+            event->Signal();
+          },
+          base::Unretained(this), base::Unretained(&done)));
+  done.Wait();
 }
 
 uint64_t WebTransportStreamImpl::BufferedDataBytes() const {
-  return quic_stream_->BufferedDataBytes();
+  if (io_runner_->BelongsToCurrentThread()) {
+    return quic_stream_->BufferedDataBytes();
+  }
+  uint64_t result;
+  base::WaitableEvent done(base::WaitableEvent::ResetPolicy::AUTOMATIC,
+                           base::WaitableEvent::InitialState::NOT_SIGNALED);
+  io_runner_->PostTask(
+      FROM_HERE,
+      base::BindOnce(
+          [](WebTransportStreamImpl const* stream, uint64_t& result,
+             base::WaitableEvent* event) {
+            result = stream->quic_stream_->BufferedDataBytes();
+            event->Signal();
+          },
+          base::Unretained(this), std::ref(result), base::Unretained(&done)));
+  done.Wait();
+  return result;
 }
 
 bool WebTransportStreamImpl::CanWrite() const {
-  return stream_->CanWrite();
+  if (io_runner_->BelongsToCurrentThread()) {
+    return stream_->CanWrite();
+  }
+  bool result;
+  base::WaitableEvent done(base::WaitableEvent::ResetPolicy::AUTOMATIC,
+                           base::WaitableEvent::InitialState::NOT_SIGNALED);
+  io_runner_->PostTask(
+      FROM_HERE,
+      base::BindOnce(
+          [](WebTransportStreamImpl const* stream, bool& result,
+             base::WaitableEvent* event) {
+            result = stream->stream_->CanWrite();
+            event->Signal();
+          },
+          base::Unretained(this), std::ref(result), base::Unretained(&done)));
+  done.Wait();
+  return result;
 }
 
 void WebTransportStreamImpl::OnCanRead() {