diff --git a/libraries/AP_HAL_ChibiOS/AnalogIn.cpp b/libraries/AP_HAL_ChibiOS/AnalogIn.cpp
index 2bd608a367..539acb7665 100644
--- a/libraries/AP_HAL_ChibiOS/AnalogIn.cpp
+++ b/libraries/AP_HAL_ChibiOS/AnalogIn.cpp
@@ -36,7 +36,17 @@ extern AP_IOMCU iomcu;
 #define ANLOGIN_DEBUGGING 0
 
 // base voltage scaling for 12 bit 3.3V ADC
-#define VOLTAGE_SCALING (3.3f/(1<<12))
+#define VOLTAGE_SCALING (3.3f / ((1 << 12) - 1))
+
+// voltage divider is usually 1/(10/(20+10))
+#ifndef HAL_IOMCU_VSERVO_SCALAR
+  #define HAL_IOMCU_VSERVO_SCALAR 3
+#endif
+
+// voltage divider is usually not present
+#ifndef HAL_IOMCU_VRSSI_SCALAR
+  #define HAL_IOMCU_VRSSI_SCALAR 1
+#endif
 
 #if ANLOGIN_DEBUGGING
  # define Debug(fmt, args ...)  do {printf("%s:%d: " fmt "\n", __FUNCTION__, __LINE__, ## args); } while(0)
@@ -462,8 +472,8 @@ void AnalogIn::_timer_tick(void)
 
 #if HAL_WITH_IO_MCU
     // now handle special inputs from IOMCU
-    _servorail_voltage = iomcu.get_vservo();
-    _rssi_voltage = iomcu.get_vrssi();
+    _servorail_voltage = iomcu.get_vservo_adc_count() * (VOLTAGE_SCALING * HAL_IOMCU_VSERVO_SCALAR);
+    _rssi_voltage = iomcu.get_vrssi_adc_count() * (VOLTAGE_SCALING *  HAL_IOMCU_VRSSI_SCALAR);
 #endif
 
     for (uint8_t i=0; i<ADC_GRP1_NUM_CHANNELS; i++) {
diff --git a/libraries/AP_HAL_ChibiOS/hwdef/Durandal/hwdef.dat b/libraries/AP_HAL_ChibiOS/hwdef/Durandal/hwdef.dat
index 4182c52b17..04c9f0fa3c 100644
--- a/libraries/AP_HAL_ChibiOS/hwdef/Durandal/hwdef.dat
+++ b/libraries/AP_HAL_ChibiOS/hwdef/Durandal/hwdef.dat
@@ -204,6 +204,9 @@ PB0 RSSI_IN ADC1 SCALE(1)
 PC0 VDD_5V_SENS ADC1 SCALE(2)
 PC1 SCALED_V3V3 ADC1 SCALE(2)
 
+# voltage divider 1/(16.9/(33+16.9))
+define HAL_IOMCU_VSERVO_SCALAR 1 / (16.9 / (33 + 16.9))
+
 # CAN bus
 PI9  CAN1_RX CAN1
 PH13 CAN1_TX CAN1