diff --git a/src/odr/internal/csv/csv_util.cpp b/src/odr/internal/csv/csv_util.cpp
index 2aef2228..e37f9e72 100644
--- a/src/odr/internal/csv/csv_util.cpp
+++ b/src/odr/internal/csv/csv_util.cpp
@@ -18,7 +18,7 @@ void csv::check_csv_file(std::istream &in) {
   auto parser = ::csv::parse(util::stream::read(in), format);
 
   // this will actually check `variable_columns`
-  for (auto &&_ : parser) {
+  for ([[maybe_unused]] auto &&_ : parser) {
   }
 
   if (parser.get_col_names().size() <= 1) {
diff --git a/src/odr/internal/json/json_util.cpp b/src/odr/internal/json/json_util.cpp
index 74155eb6..020eb0e9 100644
--- a/src/odr/internal/json/json_util.cpp
+++ b/src/odr/internal/json/json_util.cpp
@@ -6,7 +6,7 @@ namespace odr::internal {
 
 void json::check_json_file(std::istream &in) {
   // TODO limit check size
-  nlohmann::json::parse(in);
+  (void)nlohmann::json::parse(in);
   // TODO check if that even works
 }