diff --git a/include/PinMapping.h b/include/PinMapping.h
index ea9877be..614329f6 100644
--- a/include/PinMapping.h
+++ b/include/PinMapping.h
@@ -53,12 +53,12 @@ struct PinMapping_t {
     gpio_num_t led[PINMAPPING_LED_COUNT];
 
     // OpenDTU-OnBattery-specific pins below
-    int8_t victron_tx;
-    int8_t victron_rx;
-    int8_t victron_tx2;
-    int8_t victron_rx2;
-    int8_t victron_tx3;
-    int8_t victron_rx3;
+    gpio_num_t victron_tx;
+    gpio_num_t victron_rx;
+    gpio_num_t victron_tx2;
+    gpio_num_t victron_rx2;
+    gpio_num_t victron_tx3;
+    gpio_num_t victron_rx3;
     int8_t battery_rx;
     int8_t battery_rxen;
     int8_t battery_tx;
diff --git a/include/solarcharger/victron/Provider.h b/include/solarcharger/victron/Provider.h
index 6d4c507c..db571c1a 100644
--- a/include/solarcharger/victron/Provider.h
+++ b/include/solarcharger/victron/Provider.h
@@ -32,7 +32,7 @@ private:
     std::vector<String> _serialPortOwners;
     std::shared_ptr<Stats> _stats = std::make_shared<Stats>();
 
-    bool initController(int8_t rx, int8_t tx, bool logging, uint8_t instance);
+    bool initController(gpio_num_t rx, gpio_num_t tx, bool logging, uint8_t instance);
 };
 
 } // namespace SolarChargers::Victron
diff --git a/lib/VeDirectFrameHandler/VeDirectFrameHandler.cpp b/lib/VeDirectFrameHandler/VeDirectFrameHandler.cpp
index 40322f74..93ee48c9 100644
--- a/lib/VeDirectFrameHandler/VeDirectFrameHandler.cpp
+++ b/lib/VeDirectFrameHandler/VeDirectFrameHandler.cpp
@@ -62,7 +62,7 @@ VeDirectFrameHandler<T>::VeDirectFrameHandler() :
 }
 
 template<typename T>
-void VeDirectFrameHandler<T>::init(char const* who, int8_t rx, int8_t tx,
+void VeDirectFrameHandler<T>::init(char const* who, gpio_num_t rx, gpio_num_t tx,
 		Print* msgOut, bool verboseLogging, uint8_t hwSerialPort)
 {
 	_vedirectSerial = std::make_unique<HardwareSerial>(hwSerialPort);
@@ -70,7 +70,7 @@ void VeDirectFrameHandler<T>::init(char const* who, int8_t rx, int8_t tx,
 	_vedirectSerial->end(); // make sure the UART will be re-initialized
 	_vedirectSerial->begin(19200, SERIAL_8N1, rx, tx);
 	_vedirectSerial->flush();
-	_canSend = (tx != -1);
+	_canSend = (tx != GPIO_NUM_NC);
 	_msgOut = msgOut;
 	_verboseLogging = verboseLogging;
 	_debugIn = 0;
diff --git a/lib/VeDirectFrameHandler/VeDirectFrameHandler.h b/lib/VeDirectFrameHandler/VeDirectFrameHandler.h
index f66fd43e..3606284a 100644
--- a/lib/VeDirectFrameHandler/VeDirectFrameHandler.h
+++ b/lib/VeDirectFrameHandler/VeDirectFrameHandler.h
@@ -32,7 +32,7 @@ public:
 
 protected:
     VeDirectFrameHandler();
-    void init(char const* who, int8_t rx, int8_t tx, Print* msgOut,
+    void init(char const* who, gpio_num_t rx, gpio_num_t tx, Print* msgOut,
         bool verboseLogging, uint8_t hwSerialPort);
     virtual bool hexDataHandler(VeDirectHexData const &data) { return false; } // handles the disassembled hex response
 
diff --git a/lib/VeDirectFrameHandler/VeDirectMpptController.cpp b/lib/VeDirectFrameHandler/VeDirectMpptController.cpp
index d4e9dac5..99ae69ff 100644
--- a/lib/VeDirectFrameHandler/VeDirectMpptController.cpp
+++ b/lib/VeDirectFrameHandler/VeDirectMpptController.cpp
@@ -12,7 +12,7 @@
 
 //#define PROCESS_NETWORK_STATE
 
-void VeDirectMpptController::init(int8_t rx, int8_t tx, Print* msgOut,
+void VeDirectMpptController::init(gpio_num_t rx, gpio_num_t tx, Print* msgOut,
 		bool verboseLogging, uint8_t hwSerialPort)
 {
 	VeDirectFrameHandler::init("MPPT", rx, tx, msgOut,
diff --git a/lib/VeDirectFrameHandler/VeDirectMpptController.h b/lib/VeDirectFrameHandler/VeDirectMpptController.h
index ac3b9122..f3170113 100644
--- a/lib/VeDirectFrameHandler/VeDirectMpptController.h
+++ b/lib/VeDirectFrameHandler/VeDirectMpptController.h
@@ -46,7 +46,7 @@ class VeDirectMpptController : public VeDirectFrameHandler<veMpptStruct> {
 public:
     VeDirectMpptController() = default;
 
-    void init(int8_t rx, int8_t tx, Print* msgOut,
+    void init(gpio_num_t rx, gpio_num_t tx, Print* msgOut,
         bool verboseLogging, uint8_t hwSerialPort);
 
     using data_t = veMpptStruct;
diff --git a/lib/VeDirectFrameHandler/VeDirectShuntController.cpp b/lib/VeDirectFrameHandler/VeDirectShuntController.cpp
index c16b6a07..affbfda3 100644
--- a/lib/VeDirectFrameHandler/VeDirectShuntController.cpp
+++ b/lib/VeDirectFrameHandler/VeDirectShuntController.cpp
@@ -3,7 +3,7 @@
 
 VeDirectShuntController VeDirectShunt;
 
-void VeDirectShuntController::init(int8_t rx, int8_t tx, Print* msgOut,
+void VeDirectShuntController::init(gpio_num_t rx, gpio_num_t tx, Print* msgOut,
 		bool verboseLogging, uint8_t hwSerialPort)
 {
 	VeDirectFrameHandler::init("SmartShunt", rx, tx, msgOut,
diff --git a/lib/VeDirectFrameHandler/VeDirectShuntController.h b/lib/VeDirectFrameHandler/VeDirectShuntController.h
index d7bc2513..84fb5e81 100644
--- a/lib/VeDirectFrameHandler/VeDirectShuntController.h
+++ b/lib/VeDirectFrameHandler/VeDirectShuntController.h
@@ -8,7 +8,7 @@ class VeDirectShuntController : public VeDirectFrameHandler<veShuntStruct> {
 public:
     VeDirectShuntController() = default;
 
-    void init(int8_t rx, int8_t tx, Print* msgOut,
+    void init(gpio_num_t rx, gpio_num_t tx, Print* msgOut,
         bool verboseLogging, uint8_t hwSerialPort);
 
     using data_t = veShuntStruct;
diff --git a/platformio.ini b/platformio.ini
index 550f0c0c..469a4cfa 100644
--- a/platformio.ini
+++ b/platformio.ini
@@ -176,8 +176,8 @@ build_flags =
     -DHOYMILES_PIN_IRQ=GPIO_NUM_16
     -DHOYMILES_PIN_CE=GPIO_NUM_17
     -DHOYMILES_PIN_CS=GPIO_NUM_5
-    -DVICTRON_PIN_TX=21
-    -DVICTRON_PIN_RX=22
+    -DVICTRON_PIN_TX=GPIO_NUM_21
+    -DVICTRON_PIN_RX=GPIO_NUM_22
     -DPYLONTECH_PIN_RX=27
     -DPYLONTECH_PIN_TX=14
     -DHUAWEI_PIN_MISO=12
diff --git a/src/PinMapping.cpp b/src/PinMapping.cpp
index 78f7c686..40060345 100644
--- a/src/PinMapping.cpp
+++ b/src/PinMapping.cpp
@@ -139,27 +139,27 @@
 #endif // CONFIG_ETH_USE_ESP32_EMAC
 
 #ifndef VICTRON_PIN_TX
-#define VICTRON_PIN_TX -1
+#define VICTRON_PIN_TX GPIO_NUM_NC
 #endif
 
 #ifndef VICTRON_PIN_RX
-#define VICTRON_PIN_RX -1
+#define VICTRON_PIN_RX GPIO_NUM_NC
 #endif
 
 #ifndef VICTRON_PIN_TX2
-#define VICTRON_PIN_TX2 -1
+#define VICTRON_PIN_TX2 GPIO_NUM_NC
 #endif
 
 #ifndef VICTRON_PIN_RX2
-#define VICTRON_PIN_RX2 -1
+#define VICTRON_PIN_RX2 GPIO_NUM_NC
 #endif
 
 #ifndef VICTRON_PIN_TX3
-#define VICTRON_PIN_TX3 -1
+#define VICTRON_PIN_TX3 GPIO_NUM_NC
 #endif
 
 #ifndef VICTRON_PIN_RX3
-#define VICTRON_PIN_RX3 -1
+#define VICTRON_PIN_RX3 GPIO_NUM_NC
 #endif
 
 #ifndef BATTERY_PIN_RX
diff --git a/src/solarcharger/victron/Provider.cpp b/src/solarcharger/victron/Provider.cpp
index 0f5f6ebe..fa026b3a 100644
--- a/src/solarcharger/victron/Provider.cpp
+++ b/src/solarcharger/victron/Provider.cpp
@@ -38,13 +38,13 @@ void Provider::deinit()
     _serialPortOwners.clear();
 }
 
-bool Provider::initController(int8_t rx, int8_t tx, bool logging,
+bool Provider::initController(gpio_num_t rx, gpio_num_t tx, bool logging,
         uint8_t instance)
 {
     MessageOutput.printf("[VictronMppt Instance %d] rx = %d, tx = %d\r\n",
             instance, rx, tx);
 
-    if (rx < 0) {
+    if (rx <= GPIO_NUM_NC) {
         MessageOutput.printf("[VictronMppt Instance %d] invalid pin config\r\n", instance);
         return false;
     }