diff --git a/boot.c b/boot.c
index 3646a0a0..8b8236aa 100644
--- a/boot.c
+++ b/boot.c
@@ -398,7 +398,7 @@ void setup_i2c(void) __banked
 	reg_read_m(RTL837X_PIN_MUX_1);
 	for (uint8_t sfp = 0; sfp < machine.n_sfp; sfp++) {
 		uint8_t i2c = machine.sfp_port[sfp].i2c;
-		uint8_t scl_bus = (i2c >> RTL837X_REG_I2C_SCL_SHIFT) & 0x03;
+		uint8_t scl_bus = (i2c >> RTL837X_REG_I2C_SCL_SHIFT) & 0x07;
 		uint8_t sda_bus = (i2c >> RTL837X_REG_I2C_SDA_SHIFT) & 0x07;
 		print_string("Configuring I2C for SFP idx="); print_byte(sfp); print_string(" SCL="); print_byte(scl_bus); print_string(", SDA="); print_byte(sda_bus); write_char('\n');
 		switch (scl_bus) {
diff --git a/machine.c b/machine.c
index 9ce62920..5830ff27 100644
--- a/machine.c
+++ b/machine.c
@@ -5,22 +5,28 @@
 #include "rtl837x_regs.h"
 #include "rtl837x_common.h"
 
+#define I2CBUS_INVALID (7)
+// This is a MACRO to check if I2C_BUS_FROM_SDA_PIN or I2C_BUS_FROM_SCL_PIN don't return I2CBUS_INVALID.
+// When I2CBUS_INVALID is returned, compiler stops with "machine.c:<line>: error 176: sizeof applied to an incomplete type"
+#define I2CBUS_VALID(bus) (0 * sizeof(char[(bus) != I2CBUS_INVALID ? 1 : 0]))
 #define I2CBUS(sda, scl) \
-    ((uint8_t)((I2C_BUS_FROM_SCL_PIN(scl) << RTL837X_REG_I2C_SCL_SHIFT) | \
-                     (I2C_BUS_FROM_SDA_PIN(sda) << RTL837X_REG_I2C_SDA_SHIFT)))
+	((uint8_t)((I2C_BUS_FROM_SCL_PIN(scl) << RTL837X_REG_I2C_SCL_SHIFT) | \
+		   (I2C_BUS_FROM_SDA_PIN(sda) << RTL837X_REG_I2C_SDA_SHIFT) | \
+		   I2CBUS_VALID(I2C_BUS_FROM_SCL_PIN(scl)) | \
+		   I2CBUS_VALID(I2C_BUS_FROM_SDA_PIN(sda))))
 
 #define I2C_BUS_FROM_SDA_PIN(sda_pin) \
-	((sda_pin) == GPIO47_I2C_SDA0 ? (uint8_t)0 : \
-	 (sda_pin) == GPIO49_I2C_SDA1 ? (uint8_t)1 : \
-	 (sda_pin) == GPIO51_I2C_SDA2_UART1_RX ? (uint8_t)2 : \
-	 (sda_pin) == GPIO41_I2C_SDA3_MDIO1 ? (uint8_t)3 : \
-	 (sda_pin) == GPIO39_I2C_SDA4 ? (uint8_t)4 : -1)
+	((sda_pin) == GPIO47_I2C_SDA0 ? 0 : \
+	 (sda_pin) == GPIO49_I2C_SDA1 ? 1 : \
+	 (sda_pin) == GPIO51_I2C_SDA2_UART1_RX ? 2 : \
+	 (sda_pin) == GPIO41_I2C_SDA3_MDIO1 ? 3 : \
+	 (sda_pin) == GPIO39_I2C_SDA4 ? 4 : I2CBUS_INVALID)
 
 #define I2C_BUS_FROM_SCL_PIN(scl_pin) \
 	((scl_pin) == GPIO46_I2C_SCL0 ? 0 : \
 	 (scl_pin) == GPIO48_I2C_SCL1 ? 1 : \
 	 (scl_pin) == GPIO50_I2C_SCL2_UART1_TX ? 2 : \
-	 (scl_pin) == GPIO40_I2C_SCL3_MDC1 ? 3 : -1)
+	 (scl_pin) == GPIO40_I2C_SCL3_MDC1 ? 3 : I2CBUS_INVALID)
 
 #if defined(MACHINE_KP_9000_6XHML_X2) || \
 	defined(MACHINE_KP_9000_6XH_X2_V1_1) || \