diff --git a/modules/audio_device/include/test_audio_device.h b/modules/audio_device/include/test_audio_device.h
index 8413479291..e52e93c525 100644
--- a/modules/audio_device/include/test_audio_device.h
+++ b/modules/audio_device/include/test_audio_device.h
@@ -26,6 +26,9 @@
 
 namespace webrtc {
 
+// This is test API and is in development, so it can be changed/removed without
+// notice.
+
 // TestAudioDeviceModule implements an AudioDevice module that can act both as a
 // capturer and a renderer. It will use 10ms audio frames.
 class TestAudioDeviceModule : public AudioDeviceModule {