diff --git a/include/ui/GraphicBufferMapper.h b/include/ui/GraphicBufferMapper.h
index 8e93f72..001769f 100644
--- a/include/ui/GraphicBufferMapper.h
+++ b/include/ui/GraphicBufferMapper.h
@@ -39,7 +39,9 @@
 public:
     static inline GraphicBufferMapper& get() { return getInstance(); }
 
+    // This may NOT work on devices without a valid Gralloc2::Mapper.
     status_t registerBuffer(buffer_handle_t handle);
+
     status_t registerBuffer(const GraphicBuffer* buffer);
 
     status_t unregisterBuffer(buffer_handle_t handle);