diff --git a/tests/validation/validation_data.hpp b/tests/validation/validation_data.hpp
index 4abf6cca3aee6a6edd9ea7c0b8629cf62793b241..66ea5bc8cd178c2487d43f614b05ba81b8c2e7f5 100644
--- a/tests/validation/validation_data.hpp
+++ b/tests/validation/validation_data.hpp
@@ -8,7 +8,8 @@
 
 namespace testing {
 
-struct data_loader {
+class data_loader {
+public:
     // set where to find the validation JSON files
     void set_path(const std::string& path) { path_=path; }