diff --git a/include/cxx.h b/include/cxx.h
index c3037bd..f40614b 100644
--- a/include/cxx.h
+++ b/include/cxx.h
@@ -212,6 +212,7 @@
   const T *data() const noexcept;
 
 private:
+  static size_t stride() noexcept;
   void drop() noexcept;
 
   // Size and alignment statically verified by rust_vec.rs.