diff --git a/src/test_param.hpp b/src/test_param.hpp
index feddef7..8b8ad0b 100644
--- a/src/test_param.hpp
+++ b/src/test_param.hpp
@@ -224,7 +224,7 @@ class parameterized_test
     for (auto it = params_.begin(); it != params_.end(); ++it) {
       // other options will alloc
       // NOLINTNEXTLINE(cppcoreguidelines-pro-type-vararg)
-      std::sprintf(s.data(), "%zu", i++);
+      std::snprintf(s.data(), N, "%zu", i++);
       test<derived_rope_type, style_type>{value_param_name(s.data())} = g[it];
     }
   }