diff --git a/modules/audio_processing/gain_control_impl.h b/modules/audio_processing/gain_control_impl.h
index 9412e88..9dfe0f1 100644
--- a/modules/audio_processing/gain_control_impl.h
+++ b/modules/audio_processing/gain_control_impl.h
@@ -30,7 +30,7 @@
 
 class GainControlImpl : public GainControl {
  public:
-  GainControlImpl(rtc::CriticalSection* crit_capture);
+  explicit GainControlImpl(rtc::CriticalSection* crit_capture);
   ~GainControlImpl() override;
 
   void ProcessRenderAudio(rtc::ArrayView<const int16_t> packed_render_audio);