diff --git a/buffet/any_internal_impl.h b/buffet/any_internal_impl.h
index 5d93200..d875e3b 100644
--- a/buffet/any_internal_impl.h
+++ b/buffet/any_internal_impl.h
@@ -40,7 +40,7 @@
   return false;
 }
 
-struct Buffer;  // Forward declaration of data buffer container.
+class Buffer;  // Forward declaration of data buffer container.
 
 // Abstract base class for contained variant data.
 struct Data {