diff --git a/CMakeLists.txt b/CMakeLists.txt
index a5d435d..653f42d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -60,6 +60,12 @@ if(EMSCRIPTEN)
     SET(XEUS_JAVASCRIPT_USE_SHARED_XEUS ON)
     SET(XEUS_JAVASCRIPT_USE_SHARED_XEUS_JAVASCRIPT OFF)
     SET(XEUS_JAVASCRIPT_BUILD_TESTS OFF)
+
+
+    if (EMSCRIPTEN_VERSION VERSION_LESS "4.0.0")
+        # c-definitions for older emscripten versions
+        add_compile_definitions(XEUS_JAVASCRIPT_EMSCRIPTEN_OLD)
+    endif()
 endif()
 
 
diff --git a/include/xeus-javascript/convert_json.hpp b/include/xeus-javascript/convert_json.hpp
index 8f495ff..6e37385 100644
--- a/include/xeus-javascript/convert_json.hpp
+++ b/include/xeus-javascript/convert_json.hpp
@@ -47,6 +47,8 @@ struct BindingType<nl::json> {
     }
 };
 
+#ifdef XEUS_JAVASCRIPT_EMSCRIPTEN_OLD
+
 
 template <typename T>
 using is_decayed_json = std::is_same<std::decay_t<T>, nl::json>;
@@ -61,46 +63,7 @@ struct TypeID<T, enable_if_decayed_json<T> > {
     }
 };
 
-
-
-
-
-
-// template <>
-// struct TypeID<nl::json> {
-//     static constexpr TYPEID get() {
-//         return LightTypeID<val>::get();
-//     }
-// };
-
-// template <>
-// struct TypeID<const nl::json> {
-//     static constexpr TYPEID get() {
-//         return LightTypeID<val>::get();
-//     }
-// };
-
-// template <>
-// struct TypeID< nl::json  && > {
-//     static constexpr TYPEID get() {
-//         return LightTypeID<val>::get();
-//     }
-// };
-
-
-// template <>
-// struct TypeID<nl::json&> {
-//     static constexpr TYPEID get() {
-//         return LightTypeID<val>::get();
-//     }
-// };
-
-// template <>
-// struct TypeID<const nl::json&> {
-//     static constexpr TYPEID get() {
-//         return LightTypeID<val>::get();
-//     }
-// };
+#endif
 
 }  // namespace internal
 }  // namespace emscripten