diff --git a/iguana/dynamic.hpp b/iguana/dynamic.hpp
index 14ff6ed5..5c8281bb 100644
--- a/iguana/dynamic.hpp
+++ b/iguana/dynamic.hpp
@@ -35,9 +35,9 @@ struct base_impl : public base {
     }
   }
 
-  void to_json(std::string& str) override {
+  void to_json(std::string& str) const override {
     if constexpr (ENABLE_FLAG & ENABLE_JSON) {
-      to_json_adl((iguana_adl_t*)nullptr, *(static_cast<T*>(this)), str);
+      to_json_adl((iguana_adl_t*)nullptr, *(static_cast<T const*>(this)), str);
     }
     else {
       throw std::runtime_error("Json Disabled");
@@ -53,9 +53,9 @@ struct base_impl : public base {
     }
   }
 
-  void to_xml(std::string& str) override {
+  void to_xml(std::string& str) const override {
     if constexpr (ENABLE_FLAG & ENABLE_XML) {
-      to_xml_adl((iguana_adl_t*)nullptr, *(static_cast<T*>(this)), str);
+      to_xml_adl((iguana_adl_t*)nullptr, *(static_cast<T const*>(this)), str);
     }
     else {
       throw std::runtime_error("Xml Disabled");
@@ -71,9 +71,9 @@ struct base_impl : public base {
     }
   }
 
-  void to_yaml(std::string& str) override {
+  void to_yaml(std::string& str) const override {
     if constexpr (ENABLE_FLAG & ENABLE_YAML) {
-      to_yaml_adl((iguana_adl_t*)nullptr, *(static_cast<T*>(this)), str);
+      to_yaml_adl((iguana_adl_t*)nullptr, *(static_cast<T const*>(this)), str);
     }
     else {
       throw std::runtime_error("Yaml Disabled");
@@ -89,18 +89,20 @@ struct base_impl : public base {
     }
   }
 
-  iguana::detail::field_info get_field_info(std::string_view name) override {
+  iguana::detail::field_info get_field_info(
+      std::string_view name) const override {
     static constexpr auto map = iguana::get_members<T>();
     iguana::detail::field_info info{};
-    for (auto& [no, field] : map) {
+    for (auto const& [no, field] : map) {
       if (info.offset > 0) {
         break;
       }
       std::visit(
-          [&](auto val) {
+          [&](auto const& val) {
             if (val.field_name == name) {
               info.offset = member_offset((T*)this, val.member_ptr);
-              using value_type = typename decltype(val)::value_type;
+              using value_type =
+                  typename std::remove_reference_t<decltype(val)>::value_type;
 #if defined(__clang__) || defined(_MSC_VER) || \
     (defined(__GNUC__) && __GNUC__ > 8)
               info.type_name = type_string<value_type>();
@@ -136,17 +138,18 @@ struct base_impl : public base {
     static constexpr auto map = iguana::get_members<T>();
     std::any result;
 
-    for (auto [no, field] : map) {
+    for (auto const& [no, field] : map) {
       if (result.has_value()) {
         break;
       }
       std::visit(
-          [&](auto val) {
+          [&](auto const& val) {
             if (val.field_name == name) {
-              using value_type = typename decltype(val)::value_type;
+              using value_type =
+                  typename std::remove_reference_t<decltype(val)>::value_type;
               auto const offset = member_offset((T*)this, val.member_ptr);
-              auto ptr = (((char*)this) + offset);
-              result = {*((value_type*)ptr)};
+              auto ptr = (char*)this + offset;
+              result = *((value_type*)ptr);
             }
           },
           field);
diff --git a/iguana/reflection.hpp b/iguana/reflection.hpp
index d5029d7b..fb05c139 100644
--- a/iguana/reflection.hpp
+++ b/iguana/reflection.hpp
@@ -564,15 +564,16 @@ struct field_info {
 struct base {
   virtual void to_pb(std::string &str) {}
   virtual void from_pb(std::string_view str) {}
-  virtual void to_xml(std::string &str) {}
+  virtual void to_xml(std::string &str) const {}
   virtual void from_xml(std::string_view str) {}
-  virtual void to_json(std::string &str) {}
+  virtual void to_json(std::string &str) const {}
   virtual void from_json(std::string_view str) {}
-  virtual void to_yaml(std::string &str) {}
+  virtual void to_yaml(std::string &str) const {}
   virtual void from_yaml(std::string_view str) {}
   virtual std::vector<std::string_view> get_fields_name() const { return {}; }
   virtual std::any get_field_any(std::string_view name) const { return {}; }
-  virtual iguana::detail::field_info get_field_info(std::string_view name) {
+  virtual iguana::detail::field_info get_field_info(
+      std::string_view name) const {
     return {};
   }
 
diff --git a/test/test_pb.cpp b/test/test_pb.cpp
index bf784338..28bb90ff 100644
--- a/test/test_pb.cpp
+++ b/test/test_pb.cpp
@@ -237,6 +237,18 @@ struct numer_st PUBLIC(numer_st) {
 };
 REFLECTION(numer_st, a, b, c);
 
+struct MyPerson : public iguana::base_impl<MyPerson, iguana::ENABLE_JSON> {
+  MyPerson() = default;
+  MyPerson(std::string s, int d) : name(s), age(d) {}
+  std::string name;
+  int64_t age;
+  bool operator==(const MyPerson &other) const {
+    return name == other.name && age == other.age;
+  }
+};
+
+REFLECTION(MyPerson, name, age);
+
 TEST_CASE("test reflection") {
   {
     auto t = iguana::create_instance("nest1");
@@ -286,6 +298,19 @@ TEST_CASE("test reflection") {
         std::any_cast<std::variant<int, double>>(mvariant_any);
     assert(mvariant == temp_variant);
   }
+  {
+    // to_json is an const member_function now
+    MyPerson const p1{"xiaoming", 10};
+    std::string str;
+    p1.to_json(str);
+
+    // p1.to_pb(str); // compile failed
+
+    MyPerson p2;
+    p2.from_json(str);
+
+    assert(p1 == p2);
+  }
   {
     auto t = iguana::create_instance("pair_t");
     t->set_field_value("x", 12);