diff --git a/content/browser/renderer_host/media/audio_input_device_manager.cc b/content/browser/renderer_host/media/audio_input_device_manager.cc
index 2723decb20666..968bcff76ab3e 100644
--- a/content/browser/renderer_host/media/audio_input_device_manager.cc
+++ b/content/browser/renderer_host/media/audio_input_device_manager.cc
@@ -143,8 +143,13 @@ void AudioInputDeviceManager::Close(const base::UnguessableToken& session_id) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
   SendAudioLogMessage("Close({session_id=" + session_id.ToString() + "})");
   auto device = GetDevice(session_id);
-  if (device == devices_.end())
+  if (device == devices_.end()) {
+    // The asynchronous open hasn't completed yet. Record the cancellation so
+    // that OpenedOnIOThread drops the device instead of leaving an orphaned
+    // session that no DeviceRequest tracks.
+    cancelled_pending_sessions_.insert(session_id);
     return;
+  }
   const blink::mojom::MediaStreamType stream_type = device->type;
   devices_.erase(device);
 
@@ -165,6 +170,11 @@ void AudioInputDeviceManager::OpenedOnIOThread(
   DCHECK(!input_params || input_params->IsValid());
   DCHECK(!matched_output_device_id || !matched_output_device_id->empty());
 
+  if (cancelled_pending_sessions_.erase(session_id)) {
+    // Close() raced ahead of this callback; do not register the device.
+    return;
+  }
+
   SendAudioLogMessage("Opened({session_id=" + session_id.ToString() + "})");
   blink::MediaStreamDevice media_stream_device(device.type, device.id,
                                                device.name);
diff --git a/content/browser/renderer_host/media/audio_input_device_manager.h b/content/browser/renderer_host/media/audio_input_device_manager.h
index a632e8bdc96af..1a1a7435037db 100644
--- a/content/browser/renderer_host/media/audio_input_device_manager.h
+++ b/content/browser/renderer_host/media/audio_input_device_manager.h
@@ -16,6 +16,7 @@
 #include <string>
 #include <vector>
 
+#include "base/containers/flat_set.h"
 #include "base/memory/raw_ptr.h"
 #include "base/observer_list.h"
 #include "base/threading/thread.h"
@@ -73,6 +74,10 @@ class CONTENT_EXPORT AudioInputDeviceManager : public MediaStreamProvider {
   // Only accessed on Browser::IO thread.
   base::ObserverList<MediaStreamProviderListener>::Unchecked listeners_;
   blink::MediaStreamDevices devices_;
+  // Sessions for which Close() was called before the asynchronous Open()
+  // callback fired. OpenedOnIOThread() must drop these instead of adding them
+  // to `devices_`.
+  base::flat_set<base::UnguessableToken> cancelled_pending_sessions_;
 
   const raw_ptr<media::AudioSystem> audio_system_;
 };