--- src/common/json.hpp.orig	2019-04-08 14:37:06 UTC
+++ src/common/json.hpp
@@ -878,6 +878,16 @@ struct is_compatible_object_type_impl<true, RealType, 
         and std::is_constructible<typename RealType::mapped_type, typename CompatibleObjectType::mapped_type>::value;
 };
 
+template<bool B, class RealType, class CompatibleStringType>
+struct is_compatible_string_type_impl : std::false_type {};
+
+template<class RealType, class CompatibleStringType>
+struct is_compatible_string_type_impl<true, RealType, CompatibleStringType>
+{
+    static constexpr auto value =
+        std::is_same<typename RealType::value_type, typename CompatibleStringType::value_type>::value;
+};
+
 template <class BasicJsonType, class CompatibleObjectType> struct is_compatible_object_type
 {
   static auto constexpr value = is_compatible_object_type_impl<
@@ -886,6 +896,15 @@ template <class BasicJsonType, class CompatibleObjectT
       typename BasicJsonType::object_t, CompatibleObjectType>::value;
 };
 
+template<class BasicJsonType, class CompatibleStringType>
+struct is_compatible_string_type
+{
+    static auto constexpr value = is_compatible_string_type_impl <
+                                  conjunction<negation<std::is_same<void, CompatibleStringType>>,
+                                  has_value_type<CompatibleStringType>>::value,
+                                  typename BasicJsonType::string_t, CompatibleStringType >::value;
+};
+
 template <typename BasicJsonType, typename T> struct is_basic_json_nested_type
 {
   static auto constexpr value = std::is_same<T, typename BasicJsonType::iterator>::value
@@ -1137,6 +1156,25 @@ template <typename BasicJsonType> void from_json(const
   {
     JSON_THROW(type_error::create(302, "type must be string, but is " + std::string(j.type_name())));
   }
+    s = *j.template get_ptr<const typename BasicJsonType::string_t*>();
+}
+
+template <
+    typename BasicJsonType, typename CompatibleStringType,
+    enable_if_t <
+        is_compatible_string_type<BasicJsonType, CompatibleStringType>::value and
+        not std::is_same<typename BasicJsonType::string_t,
+                         CompatibleStringType>::value and
+        std::is_constructible <
+            BasicJsonType, typename CompatibleStringType::value_type >::value,
+        int > = 0 >
+void from_json(const BasicJsonType& j, CompatibleStringType& s)
+{
+    if (JSON_UNLIKELY(not j.is_string()))
+    {
+        JSON_THROW(type_error::create(302, "type must be string, but is " + std::string(j.type_name())));
+    }
+
   s = *j.template get_ptr<const typename BasicJsonType::string_t *>();
 }