diff --git a/services/surfaceflinger/RegionSamplingThread.h b/services/surfaceflinger/RegionSamplingThread.h
index d4e57bf..9796429 100644
--- a/services/surfaceflinger/RegionSamplingThread.h
+++ b/services/surfaceflinger/RegionSamplingThread.h
@@ -37,6 +37,8 @@
 class SurfaceFlinger;
 struct SamplingOffsetCallback;
 
+float sampleArea(const uint32_t* data, int32_t stride, const Rect& area);
+
 class RegionSamplingThread : public IBinder::DeathRecipient {
 public:
     struct TimingTunables {