diff --git a/include/eigenpy/std-vector.hpp b/include/eigenpy/std-vector.hpp
index 79c61a1b619ed278a2cfe88e71e4e9b3dc1a1e0f..e34668c2a0589be4418444deab30b4c4123b3e62 100644
--- a/include/eigenpy/std-vector.hpp
+++ b/include/eigenpy/std-vector.hpp
@@ -136,7 +136,7 @@ struct extract_to_eigen_ref
     : converter::extract_rvalue<Eigen::Ref<MatrixType> > {
   typedef Eigen::Ref<MatrixType> RefType;
 
- private:
+ protected:
   typedef converter::extract_rvalue<RefType> base;
 
  public: