diff --git a/ports/atmel-samd/common-hal/microcontroller/Processor.c b/ports/atmel-samd/common-hal/microcontroller/Processor.c
index 2985cf5a67..0776ff65b1 100644
--- a/ports/atmel-samd/common-hal/microcontroller/Processor.c
+++ b/ports/atmel-samd/common-hal/microcontroller/Processor.c
@@ -292,6 +292,7 @@ float common_hal_mcu_processor_get_voltage(void) {
     #endif
 
     #ifdef SAM_D5X_E5X
+    hri_supc_clear_VREF_ONDEMAND_bit(SUPC);
     hri_supc_set_VREF_SEL_bf(SUPC, SUPC_VREF_SEL_1V0_Val);
     hri_supc_set_VREF_VREFOE_bit(SUPC);