diff --git a/include/mp/nl-reader.h b/include/mp/nl-reader.h
index c53c02a69..2225df063 100644
--- a/include/mp/nl-reader.h
+++ b/include/mp/nl-reader.h
@@ -2531,7 +2531,7 @@ class NameProvider {
 
 private:
   std::vector<const char *> names_;
-  std::string gen_name_, gen_name_2_;
+  std::string gen_name_ {"_std_"}, gen_name_2_ {"_extra_"};
   internal::NameReader reader_;
   fmt::MemoryWriter writer_;
 };