diff --git a/include/ocpp/common/cistring.hpp b/include/ocpp/common/cistring.hpp
index 56d12544a..be6a08dd1 100644
--- a/include/ocpp/common/cistring.hpp
+++ b/include/ocpp/common/cistring.hpp
@@ -23,6 +23,9 @@ template <size_t L> class CiString : public String<L> {
     CiString(const char* data) : String<L>(data) {
     }
 
+    CiString(const CiString<L>& data) : String<L>(data.get()) {
+    }
+
     /// \brief Creates a string
     CiString() : String<L>() {
     }
@@ -39,7 +42,7 @@ template <size_t L> class CiString : public String<L> {
     }
 
     /// \brief Conversion operator to turn a String into std::string
-    operator std::string() {
+    operator std::string() const {
         return this->get();
     }
 };
diff --git a/lib/ocpp/v16/charge_point_configuration.cpp b/lib/ocpp/v16/charge_point_configuration.cpp
index f6574cb20..711739010 100644
--- a/lib/ocpp/v16/charge_point_configuration.cpp
+++ b/lib/ocpp/v16/charge_point_configuration.cpp
@@ -219,47 +219,47 @@ std::string ChargePointConfiguration::getChargeBoxSerialNumber() {
 }
 
 CiString<20> ChargePointConfiguration::getChargePointModel() {
-    return CiString<20>(this->config["Internal"]["ChargePointModel"]);
+    return CiString<20>(this->config["Internal"]["ChargePointModel"].get<std::string>());
 }
 std::optional<CiString<25>> ChargePointConfiguration::getChargePointSerialNumber() {
     std::optional<CiString<25>> charge_point_serial_number = std::nullopt;
     if (this->config["Internal"].contains("ChargePointSerialNumber")) {
-        charge_point_serial_number.emplace(this->config["Internal"]["ChargePointSerialNumber"]);
+        charge_point_serial_number.emplace(this->config["Internal"]["ChargePointSerialNumber"].get<std::string>());
     }
     return charge_point_serial_number;
 }
 
 CiString<20> ChargePointConfiguration::getChargePointVendor() {
-    return CiString<20>(this->config["Internal"]["ChargePointVendor"]);
+    return CiString<20>(this->config["Internal"]["ChargePointVendor"].get<std::string>());
 }
 CiString<50> ChargePointConfiguration::getFirmwareVersion() {
-    return CiString<50>(this->config["Internal"]["FirmwareVersion"]);
+    return CiString<50>(this->config["Internal"]["FirmwareVersion"].get<std::string>());
 }
 std::optional<CiString<20>> ChargePointConfiguration::getICCID() {
     std::optional<CiString<20>> iccid = std::nullopt;
     if (this->config["Internal"].contains("ICCID")) {
-        iccid.emplace(this->config["Internal"]["ICCID"]);
+        iccid.emplace(this->config["Internal"]["ICCID"].get<std::string>());
     }
     return iccid;
 }
 std::optional<CiString<20>> ChargePointConfiguration::getIMSI() {
     std::optional<CiString<20>> imsi = std::nullopt;
     if (this->config["Internal"].contains("IMSI")) {
-        imsi.emplace(this->config["Internal"]["IMSI"]);
+        imsi.emplace(this->config["Internal"]["IMSI"].get<std::string>());
     }
     return imsi;
 }
 std::optional<CiString<25>> ChargePointConfiguration::getMeterSerialNumber() {
     std::optional<CiString<25>> meter_serial_number = std::nullopt;
     if (this->config["Internal"].contains("MeterSerialNumber")) {
-        meter_serial_number.emplace(this->config["Internal"]["MeterSerialNumber"]);
+        meter_serial_number.emplace(this->config["Internal"]["MeterSerialNumber"].get<std::string>());
     }
     return meter_serial_number;
 }
 std::optional<CiString<25>> ChargePointConfiguration::getMeterType() {
     std::optional<CiString<25>> meter_type = std::nullopt;
     if (this->config["Internal"].contains("MeterType")) {
-        meter_type.emplace(this->config["Internal"]["MeterType"]);
+        meter_type.emplace(this->config["Internal"]["MeterType"].get<std::string>());
     }
     return meter_type;
 }